Showing 1–36 of 36 results for author: Boll, R

X-ray Driven Trihydrogen Formation on Silica Nanosurfaces

Authors: Samuel Sahel-Schackis, Adam Summers, Ritika Dagar, Alexandra Feinberg, Martin Grassl, Simon Dold, Rebecca Boll, Yevheniy Ovcharenko, Chris Aikens, Cesar Costa Vera, Alberto De Fanis, Avijit Duley, Felix Gerke, Daniel Jost, Regina Leiner, Michael Meyer, Ilana J. P. Molesky, Razib Obaid, Jeffrey Powell, Nils Rennhack, Björn Senfftleben, Hendrik Tackenberg, Paul Tuemmler, Sergey Usenko, Christian Peltz , et al. (7 additional authors not shown)

Abstract: The trihydrogen cation ($\mathrm{H_3^+}$) initiates the ion-molecule reactions that build molecular complexity in interstellar space. Whether its canonical formation reaction, $\mathrm{H_2^+ + H_2 \rightarrow H_3^+ + H}$, proceeds on inorganic surfaces under radiation-driven ionization has remained untested. Here we drive $\mathrm{H_3^+}$ formation on hydrated silica nanoparticles using intense 1.… ▽ More The trihydrogen cation ($\mathrm{H_3^+}$) initiates the ion-molecule reactions that build molecular complexity in interstellar space. Whether its canonical formation reaction, $\mathrm{H_2^+ + H_2 \rightarrow H_3^+ + H}$, proceeds on inorganic surfaces under radiation-driven ionization has remained untested. Here we drive $\mathrm{H_3^+}$ formation on hydrated silica nanoparticles using intense 1.88 keV X-ray pulses, combining ion velocity map imaging, electron time-of-flight spectroscopy, and single-particle coherent diffractive imaging to resolve this chemistry on individual particles. The self-induced surface electric field on the V/nm scale drives interfacial charge transfer and water fragmentation. This field is the dominant parameter governing the relative yields of $\mathrm{H^+}$, $\mathrm{H_2^+}$, and $\mathrm{H_3^+}$ across particle size, composition, and aggregation. Density functional theory and nonadiabatic quantum molecular dynamics simulations trace this field-driven charge transfer, directly analogous to band bending at semiconductor photoelectrodes. These results establish surface-field-driven charge transfer as a unifying mechanism between radiation dominated astrophysical environments and field-driven surface catalysis. △ Less

Submitted 6 August, 2026; originally announced August 2026.

Photoinduced enhancement of chemical shift sensitivity to local vibrations

Authors: Ana Martínez Gutiérrez, Oliver Alexander, Pablo Estévez Alonso, Lorenzo Paoloni, Terry Mullins, André Al-Haddad, Thomas M. Baumann, Rebecca Boll, Christoph Bostedt, Simon Dold, Alberto De Fanis, Gianluca Geloni, Markus Ilchen, Iyas Ismail, Björn Lautenschlager, Tommaso Mazza, Dooshaye Moonshiram, Solène Oberli, Dawei Peng, Ralph Püttner, Svitozar Serkez, Marc Simon, Florian Trinter, Sergey Usenko, Michael Meyer , et al. (4 additional authors not shown)

Abstract: The advent of novel free-electron laser sources enabling time-resolved x-ray photoelectron spectroscopy (tr-XPS) provides a unique opportunity to monitor local chemical environments in real time by measuring sub-eV shifts in core-electron binding energies. These shifts reflect the interplay between electronic excitation and nuclear motion, an interplay that remains largely unexplored. In our combi… ▽ More The advent of novel free-electron laser sources enabling time-resolved x-ray photoelectron spectroscopy (tr-XPS) provides a unique opportunity to monitor local chemical environments in real time by measuring sub-eV shifts in core-electron binding energies. These shifts reflect the interplay between electronic excitation and nuclear motion, an interplay that remains largely unexplored. In our combined theoretical and experimental study of fluoropyridine (C$_5$H$_4$FN), we investigate this link by monitoring the evolving chemical environment at the N and F atomic sites as the photoexcited $S_1$ state relaxes to the ground state via a conical intersection. We find that the F site responds primarily to vibrational relaxation, showing minimal sensitivity to the electronic excited state. In contrast, excitation to $S_1$ induces a measurable energy shift at the N site and significantly enhances its sensitivity to local vibrations within the ring. This behavior arises from a photoinduced redistribution of charge, which also increases the Coulomb interaction between the 1s electron at the N atom and the atomic partial charge at an adjacent C atom. This insight opens new avenues for exploring ultrafast dynamics and conical intersection pathways in more complex systems, from photostable DNA bases to light-harvesting materials. △ Less

Submitted 16 June, 2026; originally announced June 2026.

Probing the structure of cyclic hydrocarbon molecules with X-ray-induced Coulomb explosion imaging

Authors: Kurtis D. Borne, Rebecca Boll, Thomas M. Baumann, Surjendu Bhattacharyya, Martin Centurion, Keyu Chen, Benjamin Erk, Alberto De Fanis, Ruaridh Forbes, Markus Ilchen, Edwin Kukk, Huynh V. S. Lam, Xiang Li, Lingyu Ma, Tommaso Mazza, Michael Meyer, Terence Mullins, J. Pedro F. Nunes, Asami Odate, Shashank Pathak, Daniel Rivas, Philipp Schmidt, Florian Trinter, Sergey Usenko, Anbu S. Venkatachalam , et al. (5 additional authors not shown)

Abstract: Coulomb explosion imaging (CEI) is a powerful experimental technique that maps a molecule's geometric structure onto the momenta of ionic molecular fragments produced by rapid multiple ionization. Here, we apply CEI induced by pulses from an X-ray free-electron laser in order to image and distinguish complex hydrocarbon isomers with the chemical formula C7H8: toluene, cycloheptatriene, and 1,6-hep… ▽ More Coulomb explosion imaging (CEI) is a powerful experimental technique that maps a molecule's geometric structure onto the momenta of ionic molecular fragments produced by rapid multiple ionization. Here, we apply CEI induced by pulses from an X-ray free-electron laser in order to image and distinguish complex hydrocarbon isomers with the chemical formula C7H8: toluene, cycloheptatriene, and 1,6-heptadiyne. The measured fragment-ion momentum distributions show discernible differences between the three isomers and provide signatures of specific carbon and hydrogen sites in the molecule. In contrast to previous work, we demonstrate that distinct 'marker atoms' are not strictly required for constructing a meaningful molecular frame of reference for the interpretation of the momentum-space data. Our work paves the way for tracking the ultrafast motion of nuclei during isomerization reactions in pure hydrocarbons. △ Less

Submitted 3 February, 2026; originally announced February 2026.

Unraveling real-time chemical shifts in the ultrafast regime

Authors: Daniel E. Rivas, Lorenzo Paoloni, Rebecca Boll, Alberto De Fanis, Ana Martínez Gutiérrez, Tommaso Mazza, Solène Oberli, Oliver Alexander, André Al-Haddad, Thomas M. Baumann, Christoph Bostedt, Simon Dold, Gianluca Geloni, Markus Ilchen, Dooshaye Moonshiram, Daniel Rolles, Artem Rudenko, Philipp Schmidt, Svitozar Serkez, Sergey Usenko, Ángel Martín Pendás, Michael Meyer, Jesús González-Vázquez, Antonio Picón

Abstract: Traditional x-ray photoelectron spectroscopy (XPS) relies upon a direct mapping between the photoelectron binding energies and the local chemical environment, which is well-characterized by an electrostatic partial charges model for systems in equilibrium. However, the extension of this technique to out-of-equilibrium systems has been hampered by the lack of x-ray sources capable of accessing mult… ▽ More Traditional x-ray photoelectron spectroscopy (XPS) relies upon a direct mapping between the photoelectron binding energies and the local chemical environment, which is well-characterized by an electrostatic partial charges model for systems in equilibrium. However, the extension of this technique to out-of-equilibrium systems has been hampered by the lack of x-ray sources capable of accessing multiple atomic sites with high spectral and temporal resolution, as well as the lack of simple theoretical procedures to interpret the observed signals. In this work we employ multi-site XPS with a narrowband femtosecond x-ray probe to unravel different ultrafast dissociation processes of a polyatomic molecule, fluoromethane (CH$_{3}$F). We show that XPS can follow the cleavage of both the C-F and C-H bonds in real time, despite these channels lying close in binding energy. Additionally, we apply the partial charges model to describe these dynamics, and verify this extension with both advanced ab-initio calculations and experimental data. These results enable the application of this technique to out-of-equilibrium systems of higher complexity, by correlating real-time information from multiple atomic sites and interpreting the measurements through a viable theoretical modelling. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Enhanced One-Color-Two-Photon Resonant Ionization in Highly Charged Ions by Fine-Structure Effects

Authors: Moto Togawa, Chunhai Lyu, Chintan Shah, Marc Botz, Joschka Goes, Jonas Danisch, Marleen Maxton, Kai Köbnick, Filipe Grilo, Pedro Amaro, Katharina Kubicek, Mohammed Sekkal, Awad Mohamed, Rebecca Boll, Alberto De Fanis, Simon Dold, Tommaso Mazza, Jacobo Montano, Nils Rennhack, Björn Senfftleben, Sergey Usenko, Zoltan Harman, Christoph H. Keitel, Maurice Leutenegger, Michael Meyer , et al. (3 additional authors not shown)

Abstract: Ultraintense pulses from X-ray free-electron lasers can drive, within femtoseconds, multiple processes in the inner shells of atoms and molecules in all phases of matter. The ensuing complex ionization pathways of outer-shell electrons from the neutral to the final highly charged states make a comparison with theory enormously difficult. We resolve these pathways by preparing highly charged ions i… ▽ More Ultraintense pulses from X-ray free-electron lasers can drive, within femtoseconds, multiple processes in the inner shells of atoms and molecules in all phases of matter. The ensuing complex ionization pathways of outer-shell electrons from the neutral to the final highly charged states make a comparison with theory enormously difficult. We resolve these pathways by preparing highly charged ions in an electron beam ion trap before exposing them to the pulsed radiation. This reveals how relativistic fine-structure effects shift electronic energies, largely compensate the core-screening potential, and enable the consecutive, resonant absorption of two quasi-monochromatic X-ray photons that would generally be unfeasible. This doubly-resonant channel enhances the efficiency of two-photon ionization by more than two orders of magnitude, dominating in this regime the nonlinear interaction of light and matter with possible application for future precision X-ray metrology. △ Less

Submitted 7 November, 2025; originally announced November 2025.

Generative Modeling Enables Molecular Structure Retrieval from Coulomb Explosion Imaging

Authors: Xiang Li, Till Jahnke, Rebecca Boll, Jiaqi Han, Minkai Xu, Michael Meyer, Maria Novella Piancastelli, Daniel Rolles, Artem Rudenko, Florian Trinter, Thomas J. A. Wolf, Jana B. Thayer, James P. Cryan, Stefano Ermon, Phay J. Ho

Abstract: Capturing the structural changes that molecules undergo during chemical reactions in real space and time is a long-standing dream and an essential prerequisite for understanding and ultimately controlling femtochemistry. A key approach to tackle this challenging task is Coulomb explosion imaging, which benefited decisively from recently emerging high-repetition-rate X-ray free-electron laser sourc… ▽ More Capturing the structural changes that molecules undergo during chemical reactions in real space and time is a long-standing dream and an essential prerequisite for understanding and ultimately controlling femtochemistry. A key approach to tackle this challenging task is Coulomb explosion imaging, which benefited decisively from recently emerging high-repetition-rate X-ray free-electron laser sources. With this technique, information on the molecular structure is inferred from the momentum distributions of the ions produced by the rapid Coulomb explosion of molecules. Retrieving molecular structures from these distributions poses a highly non-linear inverse problem that remains unsolved for molecules consisting of more than a few atoms. Here, we address this challenge using a diffusion-based Transformer neural network. We show that the network reconstructs unknown molecular geometries from ion-momentum distributions with a mean absolute error below one Bohr radius, which is half the length of a typical chemical bond. △ Less

Submitted 13 April, 2026; v1 submitted 31 October, 2025; originally announced November 2025.

Journal ref: Nat Commun 17, 3430 (2026)

Wavelength-Dependent Photodissociation of Iodomethylbutane

Authors: Valerija Music, Felix Allum, Ludger Inhester, Philipp Schmidt, Rebecca Boll, Thomas M. Baumann, Günter Brenner, Mark Brouard, Michael Burt, Philipp V. Demekhin, Simon Dörner, Arno Ehresmann, Andreas Galler, Patrik Grychtol, David Heathcote, Denis Kargin, Mats Larsson, Jason W. L. Lee, Zheng Li, Bastian Manschwetus, Lutz Marder, Robert Mason, Michael Meyer, Huda Otto, Christopher Passow , et al. (15 additional authors not shown)

Abstract: Ultrashort XUV pulses of the Free-Electron-LASer in Hamburg (FLASH) were used to investigate laser-induced fragmentation patterns of the prototypical chiral molecule 1-iodo-2-methyl-butane (C$_5$H$_{11}$I) in a pump-probe scheme. Ion velocity-map images and mass spectra of optical-laser-induced fragmentation were obtained for subsequent FEL exposure with photon energies of 63 eV and 75 eV. These e… ▽ More Ultrashort XUV pulses of the Free-Electron-LASer in Hamburg (FLASH) were used to investigate laser-induced fragmentation patterns of the prototypical chiral molecule 1-iodo-2-methyl-butane (C$_5$H$_{11}$I) in a pump-probe scheme. Ion velocity-map images and mass spectra of optical-laser-induced fragmentation were obtained for subsequent FEL exposure with photon energies of 63 eV and 75 eV. These energies specifically address the iodine 4d edge of neutral and singly charged iodine, respectively. The presented ion spectra for two optical pump-laser wavelengths, i.e., 800 nm and 267 nm, reveal substantially different cationic fragment yields in dependence on the wavelength and intensity. For the case of 800-nm-initiated fragmentation, the molecule dissociates notably slower than for the 267-nm pump. The results underscore the importance of considering optical-laser wavelength and intensity in the dissociation dynamics of this prototypical chiral molecule that is a promising candidate for future studies of its asymmetric nature. △ Less

Submitted 23 February, 2025; originally announced February 2025.

Comments: 12 pages, 9 figures

SPRING: an effective and reliable framework for image reconstruction in single-particle Coherent Diffraction Imaging

Authors: Alessandro Colombo, Mario Sauppe, Andre Al Haddad, Kartik Ayyer, Morsal Babayan, Rebecca Boll, Ritika Dagar, Simon Dold, Thomas Fennel, Linos Hecht, Gregor Knopp, Katharina Kolatzki, Bruno Langbehn, Filipe R. N. C. Maia, Abhishek Mall, Parichita Mazumder, Tommaso Mazza, Yevheniy Ovcharenko, Ihsan Caner Polat, Dirk Raiser, Julian C. Schäfer-Zimmermann, Kirsten Schnorr, Marie Louise Schubert, Arezu Sehati, Jonas A. Sellberg , et al. (18 additional authors not shown)

Abstract: Coherent Diffraction Imaging (CDI) is an experimental technique to gain images of isolated structures by recording the light scattered off the sample. In principle, the sample density can be recovered from the scattered light field through a straightforward Fourier Transform operation. However, only the amplitude of the field is recorded, while the phase is lost during the measurement process and… ▽ More Coherent Diffraction Imaging (CDI) is an experimental technique to gain images of isolated structures by recording the light scattered off the sample. In principle, the sample density can be recovered from the scattered light field through a straightforward Fourier Transform operation. However, only the amplitude of the field is recorded, while the phase is lost during the measurement process and has to be retrieved by means of suitable, well-established phase retrieval algorithms. In this work, we present SPRING, an analysis framework tailored to X-ray Free Electron Laser (XFEL) single-shot single-particle diffraction data that implements the Memetic Phase Retrieval method to mitigate the shortcomings of conventional algorithms. We benchmark the approach on experimental data acquired in two experimental campaigns at SwissFEL and European XFEL. Imaging results on isolated nanostructures reveal unprecedented stability and resilience of the algorithm's behavior on the input parameters, as well as the capability of identifying the solution in conditions hardly treatable so far with conventional methods. A user-friendly implementation of SPRING is released as open-source software, aiming at being a reference tool for the coherent diffraction imaging community at XFEL and synchrotron facilities. △ Less

Submitted 5 March, 2025; v1 submitted 11 September, 2024; originally announced September 2024.

Comments: 30 pages, 13 figures. Authors list updated and text revised

Journal ref: npj Comput Mater 11, 265 (2025)

Differentiating Three-Dimensional Molecular Structures using Laser-induced Coulomb Explosion Imaging

Authors: Huynh Van Sa Lam, Anbu Selvam Venkatachalam, Surjendu Bhattacharyya, Keyu Chen, Kurtis Borne, Enliang Wang, Rebecca Boll, Till Jahnke, Vinod Kumarappan, Artem Rudenko, Daniel Rolles

Abstract: Coulomb explosion imaging (CEI) with x-ray free electron lasers has recently been shown to be a powerful method for obtaining detailed structural information of gas-phase planar ring molecules [R. Boll et al. Nat. Phys. 18, 423-428 (2022)]. In this Letter, we investigate the potential of CEI driven by a tabletop laser and extend this approach to differentiating three-dimensional (3D) structures. W… ▽ More Coulomb explosion imaging (CEI) with x-ray free electron lasers has recently been shown to be a powerful method for obtaining detailed structural information of gas-phase planar ring molecules [R. Boll et al. Nat. Phys. 18, 423-428 (2022)]. In this Letter, we investigate the potential of CEI driven by a tabletop laser and extend this approach to differentiating three-dimensional (3D) structures. We study the static CEI patterns of planar and nonplanar organic molecules that resemble the structures of typical products formed in ring-opening reactions. Our results reveal that each molecule exhibits a well-localized and distinctive pattern in 3D fragment-ion momentum space. We find that these patterns yield direct information about the molecular structures and can be qualitatively reproduced using a classical Coulomb explosion simulation. Our findings suggest that laser-induced CEI can serve as a robust method for differentiating molecular structures of organic ring and chain molecules. As such, it holds great promise as a method for following ultrafast structural changes, e.g., during ring-opening reactions, by tracking the motion of individual atoms in pump-probe experiments. △ Less

Submitted 15 August, 2024; originally announced August 2024.

Journal ref: Phys. Rev. Lett. 132, 123201 (2024)

Attosecond soft X-ray pulses generated by chirp-dispersed manipulation in an XFEL reveal nonlinear core-electron dynamics in neon

Authors: Lars Funke, Markus Ilchen, Svitozar Serkez, Kristina Dingel, Tommaso Mazza, Terence Mullins, Thorsten Otto, Daniel E. Rivas, Sara Savio, Peter Walter, Niclas Wieland, Lasse Wülfing, Sadia Bari, Rebecca Boll, Markus Braune, Francesca Calegari, Alberto De Fanis, Winfried Decking, Andreas Duensing, Stefan Düsterer, Felix Egun, Arno Ehresmann, Benjamin Erk, Danilo Enoque Ferreira de Lima, Andreas Galler , et al. (37 additional authors not shown)

Abstract: Free-electron lasers have demonstrated their capability of generating intense attosecond X-ray pulses, which are the key to studying electron dynamics at their natural time scale and in specifically targeted electronic states, but come at the expanse of complicated generation schemes and stochastic pulse shapes. Here, we demonstrate a novel and simple operation concept based on the manipulation of… ▽ More Free-electron lasers have demonstrated their capability of generating intense attosecond X-ray pulses, which are the key to studying electron dynamics at their natural time scale and in specifically targeted electronic states, but come at the expanse of complicated generation schemes and stochastic pulse shapes. Here, we demonstrate a novel and simple operation concept based on the manipulation of the electron-bunch chirp-dispersion and working with the full 4.5 MHz repetition rate at the European XFEL in Germany. With a high-fidelity single-shot temporal characterisation, we detect X-ray pulses with durations of down to 200 attoseconds and peak powers reaching into the terawatt regime at ~1 keV photon energy. As a direct application, we present simultaneous measurements of nonlinear X-ray-matter interaction via time-resolved electron spectroscopy. Using the derived temporal pulse information and restricting the durations to a regime where individual X-ray pulses are shorter than the single-core-hole life time in neon atoms, we reveal an otherwise hidden peak-intensity dependence in the nonlinear dynamics of double-core-hole formation. Our results open the field of attosecond science to the investigation of electronic processes not only in the ground state but also in systems driven far off their equilibrium. They shed light on highly transient intermediate steps in complex electronic dynamics and thus promise to help build the conceptual bridge between fundamental physical processes and chemical photo-reactions. △ Less

Submitted 26 May, 2026; v1 submitted 7 August, 2024; originally announced August 2024.

X-ray Coulomb explosion imaging reveals role of molecular structure in internal conversion

Authors: Till Jahnke, Sebastian Mai, Surjendu Bhattacharyya, Keyu Chen, Rebecca Boll, Maria Elena Castellani, Simon Dold, Avijit Duley, Ulrike Frühling, Alice E. Green, Markus Ilchen, Rebecca Ingle, Gregor Kastirke, Huynh Van Sa Lam, Fabiano Lever, Dennis Mayer, Tommaso Mazza, Terence Mullins, Yevheniy Ovcharenko, Björn Senfftleben, Florian Trinter, Atia Tul Noor, Sergey Usenko, Anbu Selvam Venkatachalam, Artem Rudenko , et al. (4 additional authors not shown)

Abstract: Molecular photoabsorption results in an electronic excitation/ionization which couples to the rearrangement of the nuclei. The resulting intertwined change of nuclear and electronic degrees of freedom determines the conversion of photoenergy into other molecular energy forms. Nucleobases are excellent candidates for studying such dynamics, and great effort has been taken in the past to observe the… ▽ More Molecular photoabsorption results in an electronic excitation/ionization which couples to the rearrangement of the nuclei. The resulting intertwined change of nuclear and electronic degrees of freedom determines the conversion of photoenergy into other molecular energy forms. Nucleobases are excellent candidates for studying such dynamics, and great effort has been taken in the past to observe the electronic changes induced by the initial excitation in a time-resolved manner using ultrafast electron spectroscopy. The linked geometrical changes during nucleobase photorelaxation have so far not been observed directly in time-resolved experiments. Here, we present a study on a thionucleobase, where we extract comprehensive information on the molecular rearrangement using Coulomb explosion imaging. Our measurement links the extracted deplanarization of the molecular geometry to the previously studied temporal evolution of the electronic properties of the system. In particular, the protons of the exploded molecule are well-suited messengers carrying rich information on the molecule's geometry at distinct times after the initial electronic excitation. The combination of ultrashort laser pulses to trigger molecular dynamics, intense X-ray free-electron laser pulses for the explosion of the molecule, and multi-particle coincidence detection opens new avenues for time-resolved studies of complex molecules in the gas phase. △ Less

Submitted 24 May, 2024; originally announced May 2024.

Comments: 19 pages, 8 figures

Controlled molecule injector for cold, dense, and pure molecular beams at the European x-ray free-electron laser

Authors: Lanhai He, Melby Johny, Thomas Kierspel, Karol Długołęcki, Sadia Bari, Rebecca Boll, Hubertus Bromberger, Marcello Coreno, Alberto De Fanis, Michele Di Fraia, Benjamin Erk, Mathieu Gisselbrecht, Patrik Grychtol, Per Eng-Johnsson, Tommaso Mazza, Jolijn Onvlee, Yevheniy Ovcharenko, Jovana Petrovic, Nils Rennhack, Daniel E. Rivas, Artem Rudenko, Eckart Rühl, Lucas Schwob, Marc Simon, Florian Trinter , et al. (5 additional authors not shown)

Abstract: A permanently available molecular-beam injection setup for controlled molecules (COMO) was installed and commissioned at the small quantum systems (SQS) instrument at the European x-ray free-electron laser (EuXFEL). A $b$-type electrostatic deflector allows for pure state-, size-, and isomer-selected samples of polar molecules and clusters. The source provides a rotationally cold ($T\approx1$~K) a… ▽ More A permanently available molecular-beam injection setup for controlled molecules (COMO) was installed and commissioned at the small quantum systems (SQS) instrument at the European x-ray free-electron laser (EuXFEL). A $b$-type electrostatic deflector allows for pure state-, size-, and isomer-selected samples of polar molecules and clusters. The source provides a rotationally cold ($T\approx1$~K) and dense ($ρ\approx10^8$~cm$^{-3}$) molecular beam with pulse durations up to 100~\us generated by a new version of the Even-Lavie valve. Here, a performance overview of the COMO setup is presented along with characterization experiments performed both, with an optical laser at the Center for Free-Electron-Laser Science and with x-rays at EuXFEL under burst-mode operation. COMO was designed to be attached to different instruments at the EuXFEL, in particular at the small quantum systems (SQS) and single particles, clusters, and biomolecules (SPB) instruments. This advanced controlled-molecules injection setup enables XFEL studies using highly defined samples with soft and hard x-ray FEL radiation for applications ranging from atomic, molecular, and cluster physics to elementary processes in chemistry and biology. △ Less

Submitted 10 May, 2024; originally announced May 2024.

Ultrafast Nuclear Dynamics in Double-Core Ionized Water Molecules

Authors: Iyas Ismail, Ludger Inhester, Tatiana Marchenko, Florian Trinter, Abhishek Verma, Alberto De Fanis, Anthony Ferte, Daniel E. Rivas, Dawei Peng, Dimitris Koulentianos, Edwin Kukk, Francis Penent, Gilles Doumy, Giuseppe Sansone, John D. Bozek, Kai Li, Linda Young, Markus Ilchen, Maria Novella Piancastelli, Michael Meyer, Nicolas Velasquez, Oksana Travnikova, Rebecca Boll, Renaud Guillemin, Reinhard Dorner , et al. (8 additional authors not shown)

Abstract: Double-core-hole (DCH) states in isolated water and heavy water molecules, resulting from the sequential absorption of two x-ray photons, have been investigated. A comparison of the subsequent Auger emission spectra from the two isotopes provides direct evidence of ultrafast nuclear motion during the 1.5 fs lifetime of these DCH states. Our numerical results align well with the experimental data,… ▽ More Double-core-hole (DCH) states in isolated water and heavy water molecules, resulting from the sequential absorption of two x-ray photons, have been investigated. A comparison of the subsequent Auger emission spectra from the two isotopes provides direct evidence of ultrafast nuclear motion during the 1.5 fs lifetime of these DCH states. Our numerical results align well with the experimental data, providing for various DCH states an in-depth study of the dynamics responsible of the observed isotope effect. △ Less

Submitted 11 March, 2024; v1 submitted 5 February, 2024; originally announced February 2024.

Monitoring the evolution of relative product populations at early times during a photochemical reaction

Authors: Joao Pedro Figueira Nunes, Lea Maria Ibele, Shashank Pathak, Andrew R. Attar, Surjendu Bhattacharyya, Rebecca Boll, Kurtis Borne, Martin Centurion, Benjamin Erk, Ming-Fu Lin, Ruaridh J. G. Forbes, Nate Goff, Christopher S. Hansen, Matthias Hoffmann, David M. P. Holland, Rebecca A. Ingle, Duan Luo, Sri Bhavya Muvva, Alex Reid, Arnaud Rouzée, Artem Rudenko, Sajib Kumar Saha, Xiaozhe Shen, Anbu Selvam Venkatachalam, Xijie Wang , et al. (9 additional authors not shown)

Abstract: Identifying multiple rival reaction products and transient species formed during ultrafast photochemical reactions and determining their time-evolving relative populations are key steps towards understanding and predicting photochemical outcomes. Yet, most contemporary ultrafast studies struggle with clearly identifying and quantifying competing molecular structures/species amongst the emerging re… ▽ More Identifying multiple rival reaction products and transient species formed during ultrafast photochemical reactions and determining their time-evolving relative populations are key steps towards understanding and predicting photochemical outcomes. Yet, most contemporary ultrafast studies struggle with clearly identifying and quantifying competing molecular structures/species amongst the emerging reaction products. Here, we show that mega-electronvolt ultrafast electron diffraction in combination with ab initio molecular dynamics calculations offer a powerful route to determining time-resolved populations of the various isomeric products formed after UV (266 nm) excitation of the five-membered heterocyclic molecule 2(5H)-thiophenone. This strategy provides experimental validation of the predicted high (~50%) yield of an episulfide isomer containing a strained 3-membered ring within ~1 ps of photoexcitation and highlights the rapidity of interconversion between the rival highly vibrationally excited photoproducts in their ground electronic state. △ Less

Submitted 21 November, 2023; originally announced November 2023.

Journal ref: J. Am. Chem. Soc. 2024, 146, 6, 4134-4143

Time-Resolved Coulomb Explosion Imaging Unveils Ultrafast Ring Opening of Furan

Authors: Enliang Wang, Surjendu Bhattacharyya, Keyu Chen, Kurtis Borne, Farzaneh Ziaee, Shashank Pathak, Huynh Van Sa Lam, Anbu Selvam Venkatachalam, Xiangjun Chen, Rebecca Boll, Till Jahnke, Artem Rudenko, Daniel Rolles

Abstract: Following the changes in molecular structure throughout the entirety of a chemical reaction with atomic resolution is a long-term goal in femtochemistry. Although the development of a plethora of ultrafast technique has enabled detailed investigations of the electronic and nuclear dynamics on femtosecond time scales, direct and unambiguous imaging of the nuclear motion during a reaction is still a… ▽ More Following the changes in molecular structure throughout the entirety of a chemical reaction with atomic resolution is a long-term goal in femtochemistry. Although the development of a plethora of ultrafast technique has enabled detailed investigations of the electronic and nuclear dynamics on femtosecond time scales, direct and unambiguous imaging of the nuclear motion during a reaction is still a major challenge. Here, we apply time-resolved Coulomb explosion imaging with femtosecond near-infrared pulses to visualize the ultraviolet-induced ultrafast molecular dynamics of gas-phase furan. Widely contradicting predictions and observations for this molecule have been reported in the literature. By combining the experimental Coulomb explosion imaging data with ab initio molecular dynamics and Coulomb explosion simulations, we reveal the presence of a strong ultrafast ring-opening pathway upon excitation at 198 nm that occurs within 100 fs. △ Less

Submitted 8 November, 2023; originally announced November 2023.

Comments: 18 pages, 4 figures

MSC Class: 81V55; 92E10

Multiple-core-hole resonance spectroscopy with ultraintense X-ray pulses

Authors: Aljoscha Rörig, Sang-Kil Son, Tommaso Mazza, Philipp Schmidt, Thomas M. Baumann, Benjamin Erk, Markus Ilchen, Joakim Laksman, Valerija Music, Shashank Pathak, Daniel E. Rivas, Daniel Rolles, Svitozar Serkez, Sergey Usenko, Robin Santra, Michael Meyer, Rebecca Boll

Abstract: Understanding the interaction of intense, femtosecond X-ray pulses with heavy atoms is crucial for gaining insights into the structure and dynamics of matter. One key aspect of nonlinear light-matter interaction was, so far, not studied systematically at free-electron lasers -- its dependence on the photon energy. Using resonant ion spectroscopy, we map out the transient electronic structures occu… ▽ More Understanding the interaction of intense, femtosecond X-ray pulses with heavy atoms is crucial for gaining insights into the structure and dynamics of matter. One key aspect of nonlinear light-matter interaction was, so far, not studied systematically at free-electron lasers -- its dependence on the photon energy. Using resonant ion spectroscopy, we map out the transient electronic structures occurring during the complex charge-up pathways. Massively hollow atoms featuring up to six simultaneous core holes determine the spectra at specific photon energies and charge states. We also illustrate how the influence of different X-ray pulse parameters that are usually intertwined can be partially disentangled. The extraction of resonance spectra is facilitated by the fact that the ion yields become independent of the peak fluence beyond a saturation point. Our study lays the groundwork for novel spectroscopies of transient atomic species in exotic, multiple-core-hole states that have not been explored previously. △ Less

Submitted 14 March, 2023; originally announced March 2023.

Comments: Supplementary information is included

Generation of Large Vortex-Free Superfluid Helium Nanodroplets

Authors: Anatoli Ulmer, Andrea Heilrath, Björn Senfftleben, Sean M. O. O'Connell-Lopez, Björn Kruse, Lennart Seiffert, Katharina Kolatzki, Bruno Langbehn, Andreas Hoffmann, Thomas M. Baumann, Rebecca Boll, Adam S. Chatterley, Alberto De Fanis, Benjamin Erk, Swetha Erukala, Alexandra J. Feinberg, Thomas Fennel, Patrik Grychtol, Robert Hartmann, Markus Ilchen, Manuel Izquierdo, Bennet Krebs, Markus Kuster, Tommaso Mazza, Jacobo Montaño , et al. (16 additional authors not shown)

Abstract: Superfluid helium nanodroplets are an ideal environment for the formation of metastable, self-organized dopant nanostructures. However, the presence of vortices often hinders their formation. Here, we demonstrate the generation of vortex-free helium nanodroplets and explore the size range in which they can be produced. From x-ray diffraction images of xenon-doped droplets, we identify that single… ▽ More Superfluid helium nanodroplets are an ideal environment for the formation of metastable, self-organized dopant nanostructures. However, the presence of vortices often hinders their formation. Here, we demonstrate the generation of vortex-free helium nanodroplets and explore the size range in which they can be produced. From x-ray diffraction images of xenon-doped droplets, we identify that single compact structures, assigned to vortex-free aggregation, prevail up to $10^8$ atoms per droplet. This finding builds the basis for exploring the assembly of far-from-equilibrium nanostructures at low temperatures. △ Less

Submitted 20 June, 2023; v1 submitted 14 February, 2023; originally announced February 2023.

Comments: main article: 7 pages, 3 figures; supplementary material: 12 pages, 8 figures

Two-color polarization control on angularly resolved attosecond time delays

Authors: D. I. R. Boll, L. Martini, A. Palacios, O. A. Fojón

Abstract: Measured photoionization time delays may exhibit large variations as a function of the emission angles, even for spherically symmetric targets, as shown in recent RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) experiments. The contributions from different pathways to the two-photon quantum channels can already explain the observed phase jumps that shape th… ▽ More Measured photoionization time delays may exhibit large variations as a function of the emission angles, even for spherically symmetric targets, as shown in recent RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) experiments. The contributions from different pathways to the two-photon quantum channels can already explain the observed phase jumps that shape those angular distributions. Here, we propose a simple analytical model to describe angularly-resolved RABBITT spectra as a function of the relative polarization angle between the ionizing attosecond pulse train and the assisting IR field. We demonstrate that the angular dependencies of the measured delays can be analytically predicted and the position of the phase jumps reduced to the analysis of a few relevant parameters. △ Less

Submitted 27 December, 2022; originally announced December 2022.

Comments: 10 pages, 4 figures

The Kinetic Energy of PAH Dication and Trication Dissociation Determined by Recoil-Frame Covariance Map Imaging

Authors: Jason W. L. Lee, Denis S. Tikhonov, Felix Allum, Rebecca Boll, Pragya Chopra, Benjamin Erk, Sebastian Gruet, Lanhai He, David Heathcote, Mehdi M. Kazemi, Jan Lahl, Alexander K. Lemmens, Donatella Loru, Sylvain Maclot, Robert Mason, Erland Müller, Terry Mullins, Christopher Passow, Jasper Peschel, Daniel Ramm, Amanda L. Steber, Sadia Bari, Mark Brouard, Michael Burt, Jochen Küpper , et al. (6 additional authors not shown)

Abstract: We investigated the dissociation of dications and trications of three polycyclic aromatic hydrocarbons (PAHs), fluorene, phenanthrene, and pyrene. PAHs are a family of molecules ubiquitous in space and involved in much of the chemistry of the interstellar medium. In our experiments, ions are formed by interaction with 30.3 nm extreme ultraviolet (XUV) photons, and their velocity map images are rec… ▽ More We investigated the dissociation of dications and trications of three polycyclic aromatic hydrocarbons (PAHs), fluorene, phenanthrene, and pyrene. PAHs are a family of molecules ubiquitous in space and involved in much of the chemistry of the interstellar medium. In our experiments, ions are formed by interaction with 30.3 nm extreme ultraviolet (XUV) photons, and their velocity map images are recorded using a PImMS2 multi-mass imaging sensor. Application of recoil-frame covariance analysis allows the total kinetic energy release (TKER) associated with multiple fragmentation channels to be determined to high precision, ranging 1.94-2.60 eV and 2.95-5.29 eV for the dications and trications, respectively. Experimental measurements are supported by Born-Oppenheimer molecular dynamics (BOMD) simulations. △ Less

Submitted 17 June, 2022; originally announced June 2022.

Analytical model for attosecond time delays and Fano's propensity rules in the continuum

Authors: D. I. R. Boll, L. Martini, O. A. Fojón

Abstract: Extracting single photoionization time delays associated with atomic (or molecular) species from attosecond time scale two-photon experiments usually relies on the theoretical description of continuum-continuum transitions. The available models for those processes predict a universal phase contribution, independent of the angular quantum numbers of final states. However, a recent experimental-theo… ▽ More Extracting single photoionization time delays associated with atomic (or molecular) species from attosecond time scale two-photon experiments usually relies on the theoretical description of continuum-continuum transitions. The available models for those processes predict a universal phase contribution, independent of the angular quantum numbers of final states. However, a recent experimental-theoretical study [Fuchs, \emph{et al.} Optica 7, 154 (2020)] determined a sizable time delay dependence on the angular momentum of near-threshold photoelectrons. In this study, we present an analytical model for the two-photon two-color transition matrix amplitudes that reproduces the phase dependence on the angular quantum number of final states. Finally, we show that our analytical model can also describe the generalized Fano's propensity rules [Busto, \emph{et al.} Phys. Rev. Lett. 123, 133201 (2019)] for laser-assisted photoionization. △ Less

Submitted 26 August, 2022; v1 submitted 6 May, 2022; originally announced May 2022.

Comments: 7 pages, 4 figures. Typos corrected. Equations for normalization factors added. Revised discussion in sections II, III and IV, results unchanged

Journal ref: Phys. Rev. A 106, 023116 (2022)

Single-shot MHz velocity-map-imaging using two Timepix3 cameras

Authors: Hubertus Bromberger, Christopher Passow, David Pennicard, Rebecca Boll, Jonathan Correa, Lanhai He, Melby Johny, Christina Papadopoulou, Atia Tul-Noor, Joss Wiese, Sebastian Trippel, Benjamin Erk, Jochen Küpper

Abstract: We demonstrate the application of event-driven Timepix3-based detectors in combination with a double-sided velocity-map-imaging spectrometer to record the full 3D momentum of charged particles at the free-electron-laser facility FLASH. We measured the XUV induced fragmentation of $\text{N}_2$ using 250 kHz FLASH bursts with sub-pixel spatial resolution and up to 1.7~ns temporal resolution for phot… ▽ More We demonstrate the application of event-driven Timepix3-based detectors in combination with a double-sided velocity-map-imaging spectrometer to record the full 3D momentum of charged particles at the free-electron-laser facility FLASH. We measured the XUV induced fragmentation of $\text{N}_2$ using 250 kHz FLASH bursts with sub-pixel spatial resolution and up to 1.7~ns temporal resolution for photoelectrons. To further demonstrate the capabilities of this camera at even higher repetition rates we measured single-shot images of He($1s$) photoelectrons for bursts with a repetition rate of 1 MHz. Overall, with the Timepix3 camera we overcome limitations of standard-camera technology for advanced-imaging experiments with requirements on high event-rates and high spatio-temporal resolution. △ Less

Submitted 29 November, 2021; originally announced November 2021.

Resonance-enhanced multiphoton ionization in the x-ray regime

Authors: Aaron C. LaForge, Sang-Kil Son, Debadarshini Mishra, Markus Ilchen, Stephen Duncanson, Eemeli Eronen, Edwin Kukk, Stanislaw Wirok-Stoletow, Daria Kolbasova, Peter Walter, Rebecca Boll, Alberto De Fanis, Michael Meyer, Yevheniy Ovcharenko, Daniel E. Rivas, Philipp Schmidt, Sergey Usenko, Robin Santra, Nora Berrah

Abstract: Here, we report on the nonlinear ionization of argon atoms in the short wavelength regime using ultraintense x rays from the European XFEL. After sequential multiphoton ionization, high charge states are obtained. For photon energies that are insufficient to directly ionize a $1s$ electron, a different mechanism is required to obtain ionization to Ar$^{17+}$. We propose this occurs through a two-c… ▽ More Here, we report on the nonlinear ionization of argon atoms in the short wavelength regime using ultraintense x rays from the European XFEL. After sequential multiphoton ionization, high charge states are obtained. For photon energies that are insufficient to directly ionize a $1s$ electron, a different mechanism is required to obtain ionization to Ar$^{17+}$. We propose this occurs through a two-color process where the second harmonic of the FEL pulse resonantly excites the system via a $1s \rightarrow 2p$ transition followed by ionization by the fundamental FEL pulse, which is a type of x-ray resonance-enhanced multiphoton ionization (REMPI). This resonant phenomenon occurs not only for Ar$^{16+}$, but through multiple lower charge states, where multiple ionization competes with decay lifetimes, making x-ray REMPI distinctive from conventional REMPI. With the aid of state-of-the-art theoretical calculations, we explain the effects of x-ray REMPI on the relevant ion yields and spectral profile. △ Less

Submitted 5 November, 2021; v1 submitted 15 October, 2021; originally announced October 2021.

Comments: 8 pages, 5 figures, one supplementary material (not included)

Simple model for sequential multiphoton ionization by ultra-intense x-rays

Authors: Xiang Li, Rebecca Boll, Daniel Rolles, Artem Rudenko

Abstract: A simple model for sequential multiphoton ionization by ultra-intense x-rays is presented. The derived scaling of the ion yield with pulse energy quantitatively reproduces the experimental data, which shows that the ion yield increases according to the "power law" behavior typical of multiphoton ionization, followed by saturation at high pulse energies. The calculated average time interval between… ▽ More A simple model for sequential multiphoton ionization by ultra-intense x-rays is presented. The derived scaling of the ion yield with pulse energy quantitatively reproduces the experimental data, which shows that the ion yield increases according to the "power law" behavior typical of multiphoton ionization, followed by saturation at high pulse energies. The calculated average time interval between ionizations for producing ions at a certain charge state is found to be proportional to the pulse duration and independent of all other x-ray pulse parameters. This agrees with previous studies where the kinetic energy of fragment ions with a given charge state produced by intense x-ray ionization of molecules was found to be independent of the pulse energy, but to increase with smaller pulse duration due to the smaller time interval between ionizations. △ Less

Submitted 11 December, 2020; originally announced December 2020.

Journal ref: Phys. Rev. A 104, 033115 (2021)

Tracking the Ultraviolet Photochemistry of Thiophenone During and Beyond the Initial Ultrafast Ring Opening

Authors: Shashank Pathak, Lea M. Ibele, Rebecca Boll, Carlo Callegari, Alexander Demidovich, Benjamin Erk, Raimund Feifel, Ruaridh Forbes, Michele Di Fraia, Luca Giannessi, Christopher S. Hansen, David M. P. Holland, Rebecca A. Ingle, Robert Mason, Oksana Plekan, Kevin C. Prince, Arnaud Rouzée, Richard J. Squibb, Jan Tross, Michael N. R. Ashfold, Basile F. E. Curchod, Daniel Rolles

Abstract: Photoinduced isomerization reactions, including ring-opening reactions, lie at the heart of many processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics unfolding on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoele… ▽ More Photoinduced isomerization reactions, including ring-opening reactions, lie at the heart of many processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics unfolding on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free electron laser to trace the ultrafast ring opening of gas phase thiophenone molecules following photoexcitation at 265 nm. When combined with cutting edge ab initio electronic structure and molecular dynamics calculations of both the excited and ground state molecules, the results provide unprecedented insights into both electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state is shown to be driven by ballistic SC bond extension and to be complete within 350 femtoseconds. Theory and experiment also allow clear visualization of the rich ground-state dynamics involving formation of, and interconversion between, several ring opened isomers and the reformed cyclic structure, and fragmentation (CO loss) over much longer timescales. △ Less

Submitted 14 March, 2020; v1 submitted 1 December, 2019; originally announced December 2019.

Comments: 40 pages, 21 figures Changes from the previous version: 1) Added theoretical calculations for explaining long timescale changes in shown in Figure 4(a). 2) Reworked on fitting (modelling) of the experimental data in Figure 2(b). Added another panel i.e. Figure 2(c). 3) Other minor changes and rewording in response to questions and suggestions by the referees

X-ray diffractive imaging of controlled gas-phase molecules: Toward imaging of dynamics in the molecular frame

Authors: Thomas Kierspel, Andrew Morgan, Joss Wiese, Terry Mullins, Andy Aquila, Anton Barty, Richard Bean, Rebecca Boll, Sébastien Boutet, Philip Bucksbaum, Henry N. Chapman, Lauge Christensen, Alan Fry, Mark Hunter, Jason E. Koglin, Mengning Liang, Valerio Mariani, Adi Natan, Joseph Robinson, Daniel Rolles, Artem Rudenko, Kirsten Schnorr, Henrik Stapelfeldt, Stephan Stern, Jan Thøgersen , et al. (3 additional authors not shown)

Abstract: We report experimental results on the diffractive imaging of three-dimensionally aligned 2,5-diiodothiophene molecules. The molecules were aligned by chirped near-infrared laser pulses, and their structure was probed at a photon energy of 9.5 keV ($λ\approx130 \text{pm}$) provided by the Linac Coherent Light Source. Diffracted photons were recorded on the CSPAD detector and a two-dimensional diffr… ▽ More We report experimental results on the diffractive imaging of three-dimensionally aligned 2,5-diiodothiophene molecules. The molecules were aligned by chirped near-infrared laser pulses, and their structure was probed at a photon energy of 9.5 keV ($λ\approx130 \text{pm}$) provided by the Linac Coherent Light Source. Diffracted photons were recorded on the CSPAD detector and a two-dimensional diffraction pattern of the equilibrium structure of 2,5-diiodothiophene was recorded. The retrieved distance between the two iodine atoms agrees with the quantum-chemically calculated molecular structure to within 5 %. The experimental approach allows for the imaging of intrinsic molecular dynamics in the molecular frame, albeit this requires more experimental data which should be readily available at upcoming high-repetition-rate facilities. △ Less

Submitted 7 February, 2020; v1 submitted 29 October, 2019; originally announced October 2019.

Time-resolved inner-shell photoelectron spectroscopy: from a bound molecule to an isolated atom

Authors: Felix Brauße, Gildas Goldsztejn, Kasra Amini, Rebecca Boll, Sadia Bari, Cédric Bomme, Mark Brouard, Michael Burt, Barbara Cunha de Miranda, Stefan Düsterer, Benjamin Erk, Marie Géléoc, Romain Geneaux, Alexander S. Gentleman, Renaud Guillemin, Iyas Ismail, Per Johnsson, Loïc Journel, Thomas Kierspel, Hansjochen Köckert, Jochen Küpper, Pascal Lablanquie, Jan Lahl, Jason W. L. Lee, Stuart R. Mackenzie , et al. (25 additional authors not shown)

Abstract: Due to its element- and site-specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH… ▽ More Due to its element- and site-specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH$_3$I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules. △ Less

Submitted 25 January, 2019; originally announced January 2019.

Extreme Ultraviolet Superfluorescence in Xenon and Krypton

Authors: L. Mercadier, A. Benediktovitch, C. Weninger, M. A. Blessenohl, S. Bernitt, H. Bekker, S. Dobrodey, A. Sánchez-González, B. Erk, C. Bomme, R. Boll, Z. Yin, V. P. Majety, R. Steinbrügge, M. A. Khalal, F. Penent, J. Palaudoux, P. Lablanquie, A. Rudenko, D. Rolles, J. R. Crespo López-Urrutia, N. Rohringer

Abstract: We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a high-intensity free-electron laser pulse in a cell filled with Xe or Kr gas, the medium is quasi instantaneously population-inverted by inner-shell ionization on the giant resonance followed by Auger decay. On the timescale of 100 ps a macroscopic polarization… ▽ More We present a comprehensive experimental and theoretical study on superfluorescence in the extreme ultraviolet wavelength regime. Focusing a high-intensity free-electron laser pulse in a cell filled with Xe or Kr gas, the medium is quasi instantaneously population-inverted by inner-shell ionization on the giant resonance followed by Auger decay. On the timescale of 100 ps a macroscopic polarization builds up in the medium, resulting in superfluorescent emission of several Xe and Kr lines in the forward direction. As the number of emitters in the system is increased by either raising the pressure or the pump-pulse energy, the emission shows an exponential growth of over 4 orders of magnitude and reaches saturation. With increasing yield, we observe line broadening, a manifestation of superfluorescence in the spectral domain. Our novel theoretical approach, based on a full quantum treatment of the atomic system and the irradiated field, shows quantitative agreement with the experiment and supports our interpretation. △ Less

Submitted 25 October, 2018; originally announced October 2018.

Journal ref: Phys. Rev. Lett. 123, 023201 (2019)

Photophysics of indole upon x-ray absorption

Authors: Thomas Kierspel, Cédric Bomme, Michele Di Fraia, Joss Wiese, Denis Anielski, Sadia Bari, Rebecca Boll, Benjamin Erk, Jens S. Kienitz, Nele L. M. Müller, Daniel Rolles, Jens Viefhaus, Sebastian Trippel, Jochen Küpper

Abstract: A photofragmentation study of gas-phase indole (C$_8$H$_7$N) upon single-photon ionization at a photon energy of 420 eV is presented. Indole was primarily inner-shell ionized at its nitrogen and carbon $1s$ orbitals. Electrons and ions were measured in coincidence by means of velocity map imaging. The angular relationship between ionic fragments is discussed along with the possibility to use the a… ▽ More A photofragmentation study of gas-phase indole (C$_8$H$_7$N) upon single-photon ionization at a photon energy of 420 eV is presented. Indole was primarily inner-shell ionized at its nitrogen and carbon $1s$ orbitals. Electrons and ions were measured in coincidence by means of velocity map imaging. The angular relationship between ionic fragments is discussed along with the possibility to use the angle-resolved coincidence detection to perform experiments on molecules that are strongly oriented in their recoil-frame. The coincident measurement of electrons and ions revealed fragmentation-pathway-dependent electron spectra, linking the structural fragmentation dynamics to different electronic excitations. Evidence for photoelectron-impact self-ionization was observed. △ Less

Submitted 19 July, 2018; v1 submitted 8 February, 2018; originally announced February 2018.

Comments: 11 pages, 6 figures

Journal ref: Physical Chemistry Chemical Physics, 2018, 20, 20205 - 20216

Coulomb explosion imaging of concurrent CH$_{2}$BrI photodissociation dynamics

Authors: Michael Burt, Rebecca Boll, Jason W. L. Lee, Kasra Amini, Hansjochen Köckert, Claire Vallance, Alexander S. Gentleman, Stuart R. Mackenzie, Sadia Bari, Cédric Bomme, Stefan Düsterer, Benjamin Erk, Bastian Manschwetus, Erland Müller, Dimitrios Rompotis, Evgeny Savelyev, Nora Schirmel, Simone Techert, Rolf Treusch, Jochen Küpper, Sebastian Trippel, Joss Wiese, Henrik Stapelfeldt, Barbara Cunha de Miranda, Renaud Guillemin , et al. (25 additional authors not shown)

Abstract: The dynamics following laser-induced molecular photodissociation of gas-phase CH$_{2}$BrI at 271.6 nm were investigated by time-resolved Coulomb explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH$_{2}$BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption… ▽ More The dynamics following laser-induced molecular photodissociation of gas-phase CH$_{2}$BrI at 271.6 nm were investigated by time-resolved Coulomb explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH$_{2}$BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of CH$_{2}$Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb explosion imaging as a real-time probe of chemical dynamics. △ Less

Submitted 6 October, 2017; originally announced October 2017.

Comments: 19 pages, 6 figures. Accepted for publication in Physical Review A

Probing the UV-Induced Photodissociation of CH$_\text{3}$I and C$_\text{6}$H$_\text{3}$F$_\text{2}$I with Femtosecond Time-Resolved Coulomb Explosion Imaging at FLASH

Authors: Kasra Amini, Evgeny Savelyev, Felix Brauße, Nora Berrah, Cédric Bomme, Mark Brouard, Michael Burt, Lauge Christensen, Stefan Düsterer, Benjamin Erk, Hauke Höppner, Thomas Kierspel, Faruk Krecinic, Alexandra Lauer, Jason W. L. Lee, Maria Müller, Erland Müller, Terence Mullins, Harald Redlin, Nora Schirmel, Jan Thøgersen, Simone Techert, Sven Toleikis, Rolf Treusch, Sebastian Trippel , et al. (10 additional authors not shown)

Abstract: We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from the FLASH free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267\,nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon--iodi… ▽ More We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from the FLASH free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267\,nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon--iodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local inner-shell ionization of atomic iodine in dissociating iodomethane, in contrast to non-selective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that time-resolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules. △ Less

Submitted 30 January, 2018; v1 submitted 2 August, 2017; originally announced August 2017.

Journal ref: Structural Dynamics 5, 014301 (2018)

Alignment, Orientation, and Coulomb Explosion of Difluoroiodobenzene Studied with the Pixel Imaging Mass Spectrometry (PImMS) Camera

Authors: Kasra Amini, Rebecca Boll, Alexandra Lauer, Michael Burt, Jason W L Lee, Lauge Christensen, Felix Brauße, Terence Mullins, Evgeny Savelyev, Utuq Ablikim, Nora Berrah, Cédric Bomme, Stefan Düsterer, Benjamin Erk, Hauke Höppner, Per Johnsson, Thomas Kierspel, Faruk Krecinic, Jochen Küpper, Maria Müller, Erland Müller, Harald Redlin, Arnaud Rouzée, Nora Schirmel, Jan Thøgersen , et al. (11 additional authors not shown)

Abstract: Laser-induced adiabatic alignment and mixed-field orientation of 2,6-difluoroiodobenzene (C6H3F2I) molecules are probed by Coulomb explosion imaging following either near-infrared strong-field ionization or extreme-ultraviolet multi-photon inner-shell ionization using free-electron laser pulses. The resulting photoelectrons and fragment ions are captured by a double-sided velocity map imaging spec… ▽ More Laser-induced adiabatic alignment and mixed-field orientation of 2,6-difluoroiodobenzene (C6H3F2I) molecules are probed by Coulomb explosion imaging following either near-infrared strong-field ionization or extreme-ultraviolet multi-photon inner-shell ionization using free-electron laser pulses. The resulting photoelectrons and fragment ions are captured by a double-sided velocity map imaging spectrometer and projected onto two position-sensitive detectors. The ion side of the spectrometer is equipped with the Pixel Imaging Mass Spectrometry (PImMS) camera, a time-stamping pixelated detector that can record the hit positions and arrival times of up to four ions per pixel per acquisition cycle. Thus, the time-of-flight trace and ion momentum distributions for all fragments can be recorded simultaneously. We show that we can obtain a high degree of one- and three-dimensional alignment and mixed- field orientation, and compare the Coulomb explosion process induced at both wavelengths. △ Less

Submitted 21 June, 2017; originally announced June 2017.

Journal ref: The Journal of Chemical Physics 147, 013933 (2017)

High-repetition-rate and high-photon-flux 70 eV high-harmonic source for coincidence ion imaging of gas-phase molecules

Authors: Jan Rothhardt, Steffen Hädrich, Yariv Shamir, Maxim Tschnernajew, Robert Klas, Armin Hoffmann, Getnet K. Tadesse, Arno Klenke, Thomas Gottschall, Tino Eidam, Jens Limpert, Andreas Tünnermann, Rebecca Boll, Cedric Bomme, Hatem Dachraoui, Benjamin Erk, Michele Di Fraia, Daniel A. Horke, Thomas Kierspel, Terence Mullins, Andreas Przystawik, Evgeny Savelyev, Joss Wiese, Tim Laarmann, Jochen Küpper , et al. (1 additional authors not shown)

Abstract: Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultras… ▽ More Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultrashort-pulse lasers for such studies. We present a novel high-harmonic source driven by a 100 kHz fiber laser system, which delivers 10$^{11}$ photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The combination of record-high photon flux and high repetition rate paves the way for time-resolved studies of the dissociation dynamics of inner-shell ionized molecules in a coincidence detection scheme. First coincidence measurements on CH$_3$I are shown and it is outlined how the anticipated advancement of fiber laser technology and improved sample delivery will, in the next step, allow pump-probe studies of ultrafast molecular dynamics with table-top XUV-photon sources. These table-top sources can provide significantly higher repetition rates than the currently operating free-electron lasers and they offer very high temporal resolution due to the intrinsically small timing jitter between pump and probe pulses. △ Less

Submitted 28 April, 2016; v1 submitted 11 February, 2016; originally announced February 2016.

Atoms ionized by assisted attopulses behaving as diatomic molecules

Authors: D. I. R. Boll, O. A. Fojón

Abstract: The single ionization of noble gas atoms by the combined action of XUV attopulses and an infrared laser field is theoretically investigated by means of a non-perturbative model that under certain approximations gives closed-form expressions for the angular distributions of photoelectrons. Interestingly, our model allow us to interpret the angular distributions as two-center interferences where the… ▽ More The single ionization of noble gas atoms by the combined action of XUV attopulses and an infrared laser field is theoretically investigated by means of a non-perturbative model that under certain approximations gives closed-form expressions for the angular distributions of photoelectrons. Interestingly, our model allow us to interpret the angular distributions as two-center interferences where the separation between the centers is governed by the infrared laser field. Angular distributions are compared to the available experimental data showing a good agreement. Finally, we deduce the conditions to obtain zeros in the angular distributions coming from destructive two-center interferences. △ Less

Submitted 17 December, 2015; originally announced December 2015.

Strongly aligned gas-phase molecules at Free-Electron Lasers

Authors: Thomas Kierspel, Joss Wiese, Terry Mullins, Joseph Robinson, Andy Aquila, Anton Barty, Richard Bean, Rebecca Boll, Sébastien Boutet, Philip Bucksbaum, Henry N. Chapman, Lauge Christensen, Alan Fry, Mark Hunter, Jason E. Koglin, Mengning Liang, Valerio Mariani, Andrew Morgan, Adi Natan, Vladimir Petrovic, Daniel Rolles, Artem Rudenko, Kirsten Schnorr, Henrik Stapelfeldt, Stephan Stern , et al. (5 additional authors not shown)

Abstract: We demonstrate a novel experimental implementation to strongly align molecules at full repetition rates of free-electron lasers. We utilized the available in-house laser system at the coherent x-ray imaging beamline at the Linac Coherent Light Source. Chirped laser pulses, i. e., the direct output from the regenerative amplifier of the Ti:Sa chirped pulse amplification laser system, were used to s… ▽ More We demonstrate a novel experimental implementation to strongly align molecules at full repetition rates of free-electron lasers. We utilized the available in-house laser system at the coherent x-ray imaging beamline at the Linac Coherent Light Source. Chirped laser pulses, i. e., the direct output from the regenerative amplifier of the Ti:Sa chirped pulse amplification laser system, were used to strongly align 2,5-diiodothiophene molecules in a molecular beam. The alignment laser pulses had pulse energies of a few mJ and a pulse duration of 94 ps. A degree of alignment of $\left<\cos^2\!θ_{2D}\right>$ = 0.85 was measured, limited by the intrinsic temperature of the molecular beam rather than by the available laser system. With the general availability of synchronized chirped-pulse-amplified near-infrared laser systems at short-wavelength laser facilities, our approach allows for the universal preparation of molecules tightly fixed in space for experiments with x-ray pulses. △ Less

Submitted 17 October, 2015; v1 submitted 11 June, 2015; originally announced June 2015.

Comments: 10 pages, 5 figures

Journal ref: J. Phys. B: At. Mol. Opt. Phys. 48 (2015) 204002

Imaging Molecular Structure through Femtosecond Photoelectron Diffraction on Aligned and Oriented Gas-Phase Molecules

Authors: R. Boll, A. Rouzee, M. Adolph, D. Anielski, A. Aquila, S. Bari, C. Bomme, C. Bostedt, J. D. Bozek, H. N. Chapman, L. Christensen, R. Coffee, N. Coppola, S. De, P. Decleva, S. W. Epp, B. Erk, F. Filsinger, L. Foucar, T. Gorkhover, L. Gumprecht, A. Hoemke, L. Holmegaard, P. Johnsson, J. S. Kienitz , et al. (27 additional authors not shown)

Abstract: This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray Free-Electron Laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and dissociating, laseraligned 1,4-di… ▽ More This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray Free-Electron Laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and dissociating, laseraligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments. △ Less

Submitted 29 July, 2014; originally announced July 2014.

Comments: 24 pages, 10 figures, Faraday Discussions 171

Time-Resolved Measurement of Interatomic Coulombic Decay in Ne_2

Authors: K. Schnorr, A. Senftleben, M. Kurka, A. Rudenko, L. Foucar, G. Schmid, A. Broska, T. Pfeifer, K. Meyer, D. Anielski, R. Boll, D. Rolles, M. Kübel, M. F. Kling, Y. H. Jiang, S. Mondal, T. Tachibana, K. Ueda, T. Marchenko, M. Simon, G. Brenner, R. Treusch, S. Scheit, V. Averbukh, J. Ullrich , et al. (2 additional authors not shown)

Abstract: The lifetime of interatomic Coulombic decay (ICD) [L. S. Cederbaum et al., Phys. Rev. Lett. 79, 4778 (1997)] in Ne_2 is determined via an extreme ultraviolet pump-probe experiment at the Free-Electron Laser in Hamburg. The pump pulse creates a 2s inner-shell vacancy in one of the two Ne atoms, whereupon the ionized dimer undergoes ICD resulting in a repulsive Ne^{+}(2p^{-1}) - Ne^{+}(2p^{-1}) stat… ▽ More The lifetime of interatomic Coulombic decay (ICD) [L. S. Cederbaum et al., Phys. Rev. Lett. 79, 4778 (1997)] in Ne_2 is determined via an extreme ultraviolet pump-probe experiment at the Free-Electron Laser in Hamburg. The pump pulse creates a 2s inner-shell vacancy in one of the two Ne atoms, whereupon the ionized dimer undergoes ICD resulting in a repulsive Ne^{+}(2p^{-1}) - Ne^{+}(2p^{-1}) state, which is probed with a second pulse, removing a further electron. The yield of coincident Ne^{+} - Ne^{2+} pairs is recorded as a function of the pump-probe delay, allowing us to deduce the ICD lifetime of the Ne_{2}^{+}(2s^{-1}) state to be (150 +/- 50) fs in agreement with quantum calculations. △ Less

Submitted 1 August, 2013; originally announced August 2013.

Comments: 5 pages, 3 figures, accepted by PRL on July 11th, 2013

Journal ref: Phys. Rev. Lett. 111, 093402 (2013)