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1. X-ray induced Coulomb explosion imaging of transient excited-state structural rearrangements in CS2

Author

James Unwin, Felix Allum, Mathew Britton, Ian Gabalski, Hubertus Bromberger, Mark Brouard, Philip H. Bucksbaum, Taran Driver, Nagitha Ekanayake, Diksha Garg, Eva Gougoula, David Heathcote, Andrew J. Howard, Paul Hockett, David M. P. Holland, Sonu Kumar, Chow-shing Lam, Jason W. L. Lee, Joseph McManus, Jochen Mikosch, Dennis Milesevic, Russell S. Minns, Christina C. Papadopoulou, Christopher Passow, Weronika O. Razmus, Anja Röder, Arnaud Rouzée, Michael Schuurman, Alcides Simao, Albert Stolow, Atia Tul-Noor, Claire Vallance, Tiffany Walmsley, Daniel Rolles, Benjamin Erk, Michael Burt, and Ruaridh Forbes

Subjects
Astrophysics, QB460-466, Physics, QC1-999
Abstract

Abstract Structural imaging of transient excited-state species is a key goal of molecular physics, promising to unveil rich information about the dynamics underpinning photochemical transformations. However, separating the electronic and nuclear contributions to the spectroscopic observables is challenging, and typically requires the application of high-level theory. Here, we employ site-selective ionisation via ultrashort soft X-ray pulses and time-resolved Coulomb explosion imaging to interrogate structural dynamics of the ultraviolet photochemistry of carbon disulfide. This prototypical system exhibits the complex motifs of polyatomic photochemistry, including strong non-adiabatic couplings, vibrational mode couplings, and intersystem crossing. Immediately following photoexcitation, we observe Coulomb explosion signatures of highly bent and stretched excited-state geometries involved in the photodissociation. Aided by a model to interpret such changes, we build a comprehensive picture of the photoinduced nuclear dynamics that follows initial bending and stretching motions, as the reaction proceeds towards photodissociation.

Published
2023
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2. Filming enhanced ionization in an ultrafast triatomic slingshot

Author

Andrew J. Howard, Mathew Britton, Zachary L. Streeter, Chuan Cheng, Ruaridh Forbes, Joshua L. Reynolds, Felix Allum, Gregory A. McCracken, Ian Gabalski, Robert R. Lucchese, C. William McCurdy, Thomas Weinacht, and Philip H. Bucksbaum

Subjects
Chemistry, QD1-999
Abstract

Abstract Filming atomic motion within molecules is an active pursuit of molecular physics and quantum chemistry. A promising method is laser-induced Coulomb Explosion Imaging (CEI) where a laser pulse rapidly ionizes many electrons from a molecule, causing the remaining ions to undergo Coulomb repulsion. The ion momenta are used to reconstruct the molecular geometry which is tracked over time (i.e., filmed) by ionizing at an adjustable delay with respect to the start of interatomic motion. Results are distorted, however, by ultrafast motion during the ionizing pulse. We studied this effect in water and filmed the rapid “slingshot” motion that enhances ionization and distorts CEI results. Our investigation uncovered both the geometry and mechanism of the enhancement which may inform CEI experiments in many other polyatomic molecules.

Published
2023
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3. A localized view on molecular dissociation via electron-ion partial covariance

Author

Felix Allum, Valerija Music, Ludger Inhester, Rebecca Boll, Benjamin Erk, Philipp Schmidt, Thomas M. Baumann, Günter Brenner, 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, Rudolf Pietschnig, Daniel Ramm, Kaja Schubert, Lucas Schwob, Richard D. Thomas, Claire Vallance, Igor Vidanović, Clemens von Korff Schmising, René Wagner, Peter Walter, Vitali Zhaunerchyk, Daniel Rolles, Sadia Bari, Mark Brouard, and Markus Ilchen

Subjects
Chemistry, QD1-999
Abstract

Coincidence experiments at free-electron lasers enable time resolved site-specific investigations of molecular photochemistry at high signal rates, but isolating individual dissociation processes still poses a considerable technical challenge. Here, the authors use electron-ion partial covariance imaging to isolate otherwise elusive chemical shifts in UV-induced photofragmentation pathways of the prototypical chiral molecule 1-iodo-2-methylbutane.

Published
2022
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4. Photon energy-resolved velocity map imaging from spectral domain ghost imaging

Author

Jun Wang, Taran Driver, Felix Allum, Christina C Papadopoulou, Christopher Passow, Günter Brenner, Siqi Li, Stefan Düsterer, Atia Tul Noor, Sonu Kumar, Philip H Bucksbaum, Benjamin Erk, Ruaridh Forbes, and James P Cryan

Subjects
x-ray free electron laser, velocity map imaging, spectral-domain ghost imaging, Science, Physics, QC1-999
Abstract

We present an approach that combines photon spectrum correlation analysis with the reconstruction of three-dimensional momentum distribution from velocity map images in an efficient, single-step procedure. We demonstrate its efficacy with the results from the photoionization of the 2 p -shell of argon using the Free-electron LASer in Hamburg free-electron laser (FEL). Distinct spectral features due to the spin-orbit splitting of Ar $^+(2p^{-1})$ are resolved, despite the large average bandwidth of the ionizing pulses from the FEL. This demonstrates a clear advantage over the conventional analysis method, and it will be broadly beneficial for velocity map imaging experiments with FEL sources. The retrieved linewidth of the binding energy spectrum approaches the resolution limitation prescribed by the spectrometers used to collect the data. Our approach presents a path to extend spectral-domain ghost imaging to the case where the photoproduct observable is high-dimensional.

Published
2023
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5. Multiparticle cumulant mapping for coulomb explosion imaging

Author

Chuan Cheng, Leszek J. Frasinski, Gönenç Moğol, Felix Allum, Andrew J. Howard, Daniel Rolles, Philip H. Bucksbaum, Mark Brouard, Ruaridh Forbes, and Thomas Weinacht

Subjects
General Physics and Astronomy
Abstract

We extend covariance velocity map ion imaging to four particles, establishing cumulant mapping and allowing for measurements that provide insights usually associated with coincidence detection, but at much higher count rates. Without correction, a fourfold covariance analysis is contaminated by the pairwise correlations of uncorrelated events, but we have addressed this with the calculation of a full cumulant, which subtracts pairwise correlations. We demonstrate the approach on the four-body breakup of formaldehyde following strong field multiple ionization in few-cycle laser pulses. We compare Coulomb explosion imaging for two different pulse durations (30 and 6 fs), highlighting the dynamics that can take place on ultrafast timescales. These results have important implications for Coulomb explosion imaging as a tool for studying ultrafast structural changes in molecules, a capability that is especially desirable for high-count-rate x-ray free-electron laser experiments.

Published
2023

6. Photoionization and photofragmentation dynamics of I2 in intense laser fields: a velocity-map imaging study

Author

Felix Allum, Joseph McManus, Oskar Denby, Michael Burt, and Mark Brouard

Subjects
Physical and Theoretical Chemistry
Abstract

The photoionization and photofragmentation dynamics of I2in intense femtosecond near-infrared laser fields were studied using velocity-map imaging of cations, electrons, and anions. A series of photofragmentation pathways originating from different cationic electronic states were observed following single ionization, leading to I+fragments with distinct kinetic energies, which could not be resolved in previous studies. Photoelectron spectra indicate that these high-lying dissociative states are primarily produced through nonresonant ionization from several molecular orbitals (MO) of the neutral. The photoelectron spectra also show clear signatures of resonant ionization pathways (Freeman resonances) to low-lying bound ionic states via Rydberg states of the neutral moiety. To investigate the role of these Rydberg states further, we imaged anionic products (I–) formed through ion-pair dissociations of neutral molecules excited to these Rydberg states by the intense femtosecond laser pulse. Collectively, these results shed significant new light on the complex dynamics of I2molecules in intense laser fields and on the important role of neutral Rydberg states in a full description of strong-field phenomena in molecules.

Published
2023

8. Multi-Particle Three-Dimensional Covariance Imaging: 'Coincidence' Insights into the Many-Body Fragmentation of Strong-Field Ionized D2O

Author

Thomas Weinacht, Mark Brouard, Ruaridh Forbes, Felix Allum, Chuan Cheng, Philip H. Bucksbaum, and Andrew J. Howard

Subjects
Physics, Detector, Covariance, Laser, Coincidence, law.invention, Computational physics, Data acquisition, Fragmentation (mass spectrometry), Orders of magnitude (time), law, Ionization, General Materials Science, Physics::Chemical Physics, Physical and Theoretical Chemistry
Abstract

We demonstrate the applicability of covariance analysis to three-dimensional velocity-map imaging experiments using a fast time stamping detector. Studying the photofragmentation of strong-field doubly ionized D2O molecules, we show that combining high count rate measurements with covariance analysis yields the same level of information typically limited to the “gold standard” of true, low count rate coincidence experiments, when averaging over a large ensemble of photofragmentation events. This increases the effective data acquisition rate by approximately 2 orders of magnitude, enabling a new class of experimental studies. This is illustrated through an investigation into the dependence of three-body D2O2+ dissociation on the intensity of the ionizing laser, revealing mechanistic insights into the nuclear dynamics driven during the laser pulse. The experimental methodology laid out, with its drastic reduction in acquisition time, is expected to be of great benefit to future photofragment imaging studies.

Published
2021
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9. Ultrafast probing of charge transfer dynamics with an XUV free-electron laser

Author

Felix Allum, Yoshiaki Kumagai, Kiyonobu Nagaya, James Harries, Hiroshi Iwayama, Akinobu Niozu, Mike Ashfold, Matthew Britton, Phillip Bucksbaum, Mark Brouard, Michael Burt, David Heathcote, Paul Hockett, Yusong Liu, Edwin Kukk, Jason Lee, Joseph McManus, Dennis Milesevic, Russell Minns, Johannes Niskannen, Andrew Orr-Ewing, Daniel Rolles, Artem Rudenko, Kiyoshi Ueda, James Unwin, Claire Vallance, Tiffany Walmsley, and Ruaridh Forbes

Published
2022
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13. The Kinetic Energy of PAH Dication and Trication Dissociation Determined by Recoil-Frame Covariance Map Imaging

Author

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, Per Eng-Johnsson, Anouk M. Rijs, Daniel Rolles, Claire Vallance, Bastian Manschwetus, and Melanie Schnell

Subjects
Chemical Physics (physics.chem-ph), Physics - Chemical Physics, ddc:540, General Physics and Astronomy, FOS: Physical sciences, Physical and Theoretical Chemistry
Abstract

Physical chemistry, chemical physics 24, 23096 - 23105 (2022). doi:10.1039/D2CP02252D special issue: "Ions, electrons, coincidences and dynamics: Festschrift for John H.D. Eland", 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. Ions are formed by ionization with 30.3 nm extreme ultraviolet (XUV) photons, and their velocity map images are recorded using a PImMS 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. Experimental measurements are supported by Born-Oppenheimer molecular dynamics (BOMD) molecular dynamics simulations., Published by RSC Publ., Cambridge

Published
2022
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14. UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses

Author

Hansjochen Köckert, Jason W L Lee, Felix Allum, Kasra Amini, Sadia Bari, Cédric Bomme, Felix Brauße, Mark Brouard, Michael Burt, Barbara Cunha de Miranda, Stefan Düsterer, Per Eng-Johnsson, Benjamin Erk, Marie Géléoc, Romain Geneaux, Alexander S Gentleman, Renaud Guillemin, Gildas Goldsztejn, David M P Holland, Iyas Ismail, Loïc Journel, Thomas Kierspel, Jochen Küpper, Jan Lahl, Stuart R Mackenzie, Sylvain Maclot, Bastian Manschwetus, Andrey S Mereshchenko, Terence Mullins, Pavel K Olshin, Jérôme Palaudoux, Francis Penent, Maria Novella Piancastelli, Dimitrios Rompotis, Arnaud Rouzée, Thierry Ruchon, Artem Rudenko, Nora Schirmel, Marc Simon, Simone Techert, Oksana Travnikova, Sebastian Trippel, Claire Vallance, Enliang Wang, Joss Wiese, Farzaneh Ziaee, Tatiana Marchenko, Daniel Rolles, Rebecca Boll, University of Oxford, Deutsches Elektronen-Synchrotron DESY, Physique à Haute Intensité (PHI), Institut Rayonnement Matière de Saclay (IRAMIS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Laboratoire Interactions, Dynamiques et Lasers (ex SPAM) (LIDyl), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Max-Born-institut, Berlin, Dynamique Réactionnelle (DyR), Deutsches Elektronen-Synchrotron [Hamburg] (DESY), Lund University [Lund], Laboratoire Interactions, Dynamiques et Lasers (ex SPAM) (LIDyl), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Chimie Physique - Matière et Rayonnement (LCPMR), Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Center for Free-Electron Laser Science (CFEL), Universität Hamburg (UHH), Deutsches Elektronen-Synchrotron [Zeuthen] (DESY), Helmholtz-Gemeinschaft = Helmholtz Association, Saint Petersburg State University (SPBU), Department of Physics and Astronomy [Uppsala], Uppsala University, European XFEL Gmbh, Kansas State University, and ANR-16-CE30-0001,ATTOMEMUCHO,Dynamique électronique attoseconde dans les molécules organiques isolées par la spectroscopie 'core-hole clock'(2016)

Subjects
[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, Atom and Molecular Physics and Optics, charge transfer, free-electron lasers, Atom- och molekylfysik och optik, ddc:530, Condensed Matter Physics, Atomic and Molecular Physics, and Optics, ultrafast molecular dynamics
Abstract

Journal of physics / B 55(1), 014001 (2022). doi:10.1088/1361-6455/ac489d, The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH$_2$BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump���XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH$_2$Br radicals produced by C���I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH$_2$BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way., Published by IOP Publ., Bristol

Published
2022
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15. Ultrafast Molecular Imaging Using 4-Fold Covariance: Coincidence Insight with Covariance Speed

Author

Chuan Cheng, Leszek J. Frasinski, Gönenç Moğol, Felix Allum, Andrew J. Howard, Philip H. Bucksbaum, Mark Brouard, Ruaridh Forbes, and Thomas Weinacht

Abstract

We develop mathematical tools to compute higher order covariances in charged particle detection, and demonstrate fourfold covariance measurements for molecular imaging with intense ultrafast laser pulses.

Published
2022
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16. Disentangling sequential and concerted fragmentations of molecular polycations with covariant native frame analysis

Author

Joseph W. McManus, Tiffany Walmsley, Kiyonobu Nagaya, James R. Harries, Yoshiaki Kumagai, Hiroshi Iwayama, Michael N.R. Ashfold, Mathew Britton, Philip H. Bucksbaum, Briony Downes-Ward, Taran Driver, David Heathcote, Paul Hockett, Andrew J. Howard, Edwin Kukk, Jason W. L. Lee, Yusong Liu, Dennis Milesevic, Russell S. Minns, Akinobu Niozu, Johannes Niskanen, Andrew J. Orr-Ewing, Shigeki Owada, Daniel Rolles, Patrick A. Robertson, Artem Rudenko, Kiyoshi Ueda, James Unwin, Claire Vallance, Michael Burt, Mark Brouard, Ruaridh Forbes, and Felix Allum

Subjects
ddc:540, General Physics and Astronomy, Physical and Theoretical Chemistry
Abstract

Physical chemistry, chemical physics 24(37), 22699 - 22709 (2022). doi:10.1039/D2CP03029B, We present results from an experimental ion imaging study into the fragmentation dynamics of 1-iodopropane and 2-iodopropane following interaction with extreme ultraviolet intense femtosecond laser pulses with a photon energy of 95 eV. Using covariance imaging analysis, a range of observed fragmentation pathways of the resulting polycations can be isolated and interrogated in detail at relatively high ion count rates (∼12 ions shot$^{−1}$). By incorporating the recently developed native frames analysis approach into the three-dimensional covariance imaging procedure, contributions from three-body concerted and sequential fragmentation mechanisms can be isolated. The angular distribution of the fragment ions is much more complex than in previously reported studies for triatomic polycations, and differs substantially between the two isomeric species. With support of simple simulations of the dissociation channels of interest, detailed physical insights into the fragmentation dynamics are obtained, including how the initial dissociation step in a sequential mechanism influences rovibrational dynamics in the metastable intermediate ion and how signatures of this nuclear motion manifest in the measured signals., Published by RSC Publ., Cambridge

Published
2022
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17. Multi-Particle Three-Dimensional Covariance Imaging: 'Coincidence' Insights into the Many-Body Fragmentation of Strong-Field Ionized D

Author

Felix, Allum, Chuan, Cheng, Andrew J, Howard, Philip H, Bucksbaum, Mark, Brouard, Thomas, Weinacht, and Ruaridh, Forbes

Abstract

We demonstrate the applicability of covariance analysis to three-dimensional velocity-map imaging experiments using a fast time stamping detector. Studying the photofragmentation of strong-field doubly ionized D

Published
2021

18. Time-resolved diffraction: general discussion

Author

Varun Makhija, Michael N. R. Ashfold, Evgenii Titov, Mats Simmermacher, Raphael J. F. Berger, Elke Fasshauer, Mikhail A. Ivanov, Gilbert Grell, Peter M. Weber, Gopal Dixit, Kasra Amini, Ingo Fischer, Dipanshu Bansal, Felix Allum, Haiwang Yong, Kenneth Lopata, Oleg Kornilov, Daniel B. Durham, Daniel M. Neumark, Adi Natan, Andrés Moreno Carrascosa, Taro Sekikawa, Adam Kirrander, Daniel Rolles, S. Pratt, A. S. Maxwell, Anja Röder, Linda Young, Lingyu Ma, Albert Stolow, Martin Centurion, Christian Kuttner, J. P. F. Nunes, Jean Christophe Tremblay, Jan M. Rost, Laboratoire de Physique et Chimie Théoriques (LPCT), and Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Diffraction, Materials science, business.industry, 02 engineering and technology, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, 0104 chemical sciences, Computational physics, [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry, Text mining, [PHYS.QPHY]Physics [physics]/Quantum Physics [quant-ph], Physical and Theoretical Chemistry, 0210 nano-technology, business, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2021
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19. Strong-field physics: general discussion

Author

Elke Fasshauer, Evgenii Titov, Arnaud Rouzée, Misha Ivanov, Toshinori Suzuki, Gopal Dixit, Alicia Palacios, Linda Young, Lingfeng Ge, Stephen T. Pratt, Rituparna Das, Anja Röder, Huan Doan, Nina Rohringer, Felix Allum, A. S. Maxwell, Fernando Martín, Oleg Kornilov, Jean Christophe Tremblay, Haiwang Yong, Kyle Acheson, Christian Kuttner, Gilbert Grell, Jochen Küpper, and Nicola Mayer

Subjects
Strong field, Physical and Theoretical Chemistry, Data science
Published
2021

20. Ultrafast X-ray science: general discussion

Author

Misha Ivanov, Thomas Pfeifer, Adam Kirrander, Francesca Calegari, Gilbert Grell, Thomas Wolf, Spiridoula Matsika, Daniel M. Neumark, Albert Stolow, Martin Centurion, Anja Röder, Andrea Oyarzun, Adi Natan, Andrés Moreno Carrascosa, Jochen Küpper, Christian Kuttner, Asami Odate, Gopal Dixit, Stefano M. Cavaletto, Evgenii Titov, A. S. Maxwell, Arnaud Rouzée, Alicia Palacios, Jan M. Rost, Peter M. Weber, Oleg Kornilov, J. P. Marangos, Ingo Fischer, Russell S. Minns, Felix Allum, Ruaridh Forbes, and Elke Fasshauer

Subjects
Physics, Optics, business.industry, X-ray, Physical and Theoretical Chemistry, business, Ultrashort pulse
Published
2021

21. Multi-channel photodissociation and XUV-induced charge transfer dynamics in strong-field-ionized methyl iodide studied with time-resolved recoil-frame covariance imaging

Author

Johannes Niskanen, Kiyoshi Ueda, Jordan O'Neal, Joanne Woodhouse, Hiroshi Iwayama, Nicholas Werby, Claire Vallance, Leon Kaiser, Taran Driver, Felix Allum, Mark Brouard, Artem Rudenko, Michael Burt, Briony Downes-Ward, Farzaneh Ziaee, Russell S. Minns, XiaoJing Liu, James D. Pickering, Yudai Ishimura, Shu Saito, Daehyun You, Edwin Kukk, Shigeki Owada, Philip H. Bucksbaum, Akinobu Niozu, Kiyonobu Nagaya, Sven Grundmann, Daniel Rolles, James R. Harries, Jongmin Lee, Ruaridh Forbes, and Nils Anders

Subjects
Materials science, Photodissociation, 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, Ion, SACLA, chemistry.chemical_compound, Fragmentation (mass spectrometry), chemistry, Extreme ultraviolet, Ionization, 0103 physical sciences, Physics::Atomic and Molecular Clusters, Physical and Theoretical Chemistry, Atomic physics, 010306 general physics, 0210 nano-technology, Ultrashort pulse, Methyl iodide
Abstract

The photodissociation dynamics of strong-field ionized methyl iodide (\ce{CH3I}) were probed using intense extreme ultraviolet (XUV) radiation produced by the SPring-8 Angstrom Compact free electron LAser (SACLA). Strong-field ionization and subsequent fragmentation of CH3I was initiated by an intense femtosecond infrared (IR) pulse. The ensuing fragmentation and charge-transfer processes following multiple ionization by the XUV pulse at a range of pump-probe delays were followed in a multi-mass ion velocity-map imaging (VMI) experiment. Simultaneous imaging of a wide range of resultant ions allowed for additional insight into the complex dynamics by elucidating correlations between the momenta of different fragment ions using time-resolved recoil-frame covariance imaging analysis. The comprehensive picture of the photodynamics that can be extracted provides promising evidence that the techniques described here could be applied to study ultrafast photochemistry in a range of molecular systems at high count rates using state-of-the-art advanced light sources.

Published
2021

22. Post extraction inversion slice imaging for 3D velocity map imaging experiments

Author

Craig S. Slater, Eleanor Squires, Mark Brouard, Michael Burt, Robert Mason, Benjamin Winter, and Felix Allum

Subjects
Materials science, 010304 chemical physics, Photodissociation, Biophysics, Inversion (meteorology), 010402 general chemistry, Condensed Matter Physics, 01 natural sciences, 0104 chemical sciences, Computational physics, Ion, Physics::Plasma Physics, 0103 physical sciences, Wafer, Physical and Theoretical Chemistry, Molecular Biology, Voltage
Abstract

An experimental configuration for velocity map ion imaging experiments is presented, in which a pulsed voltage defocusses the ion Newton sphere along the time-of-flight axis. This significantly spreads the times-of-flight for ions with the same mass-to-charge ratio, allowing for either sliced or three-dimensional velocity imaging with high slicing resolution along the time-of-flight axis. The technique is coupled to an event-triggered, position-sensitive sensor, enabling full three-dimensional Newton sphere imaging at high count rates, with significantly improved slicing resolution (∼1–2%) compared to previous DC slicing approaches. Good slice imaging conditions can be brought about at relatively high extraction voltages, circumventing issues regarding image size, stray fields, and poor detection efficiency when operating at low extraction voltages. The method, termed Post Extraction Inversion Slice Imaging (PEISI) was optimised through ion trajectory simulations and experimentally verified on the well-studied photodissociation of OCS at around 230 nm. We demonstrate that this approach is suitable for recording full 3D angular distributions of systems lacking an axis of cylindrical symmetry in the detector plane, where conventional image inversion techniques are invalid. This method could be useful in a range of systems lacking cylindrical symmetry, including studies into angular momentum polarisation and bimolecular scattering.

Published
2020
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23. Time-resolved site-selective imaging of predissociation and charge transfer dynamics: the CH3I B-band

Author

Bastian Manschwetus, Kurtis Borne, Andrew J. Howard, Arnaud Rouzée, Felix Allum, Rebecca Boll, Jongmin Lee, Sadia Bari, Daniel E. Rivas, Christopher Passow, Mark Brouard, Ruaridh Forbes, Robert Mason, Farzaneh Ziaee, Michael Burt, Claire Vallance, Philip H. Bucksbaum, Nagitha Ekanayake, Benjamin Erk, Aljoscha Rörig, Daniel Rolles, Per Johnsson, and Jasper Peschel

Subjects
Physics, 010304 chemical physics, Photodissociation, Condensed Matter Physics, Kinetic energy, 01 natural sciences, Atomic and Molecular Physics, and Optics, Dissociation (chemistry), Ionization, Picosecond, Extreme ultraviolet, 0103 physical sciences, Physics::Atomic and Molecular Clusters, ddc:530, Rydberg state, Atomic physics, 010306 general physics, Excitation
Abstract

Journal of physics / B 53(22), 224001 (2020). doi:10.1088/1361-6455/abb1fd, The predissociation dynamics of the 6s (B$^2$E) Rydberg state of gas-phase CH$_3$I were investigated by time-resolved Coulomb-explosion imaging using extreme ultraviolet (XUV) free-electron laser pulses. Inner-shell ionization at the iodine 4d edge was utilized to provide a site-specific probe of the ensuing dynamics. The combination of a velocity-map imaging (VMI) spectrometer coupled with the pixel imaging mass spectrometry (PImMS) camera permitted three-dimensional ionic fragment momenta to be recorded simultaneously for a wide range of iodine charge states. In accord with previous studies, initial excitation at 201.2 nm results in internal conversion and subsequent dissociation on the lower-lying A-state surface on a picosecond time scale. Examination of the time-dependent yield of low kinetic energy iodine fragments yields mechanistic insights into the predissociation and subsequent charge transfer following multiple ionization of the iodine products. The effect of charge transfer was observed through differing delay-dependencies of the various iodine charge states, from which critical internuclear distances for charge transfer could be inferred and compared to a classical over-the-barrier model. Time-dependent photofragment angular anisotropy parameters were extracted from the central slice of the Newton sphere, without Abel inversion, and highlight the effect of rotation of the parent molecule before dissociation, as observed in previous works. Our results demonstrate the ability to perform three-dimensional ion imaging at high event rates and showcase the potential benefits of this approach, particularly in relation to further time-resolved studies at free-electron laser facilities., Published by IOP Publ., Bristol

Published
2020
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24. Ultrafast Structural Changes in Chiral Molecules Measured with Free-Electron Lasers

Author

M. Larsson, Michael Burt, A. Lutmann, Claire Vallance, Gregor Hartmann, Mark Brouard, R. Coffee, Lucas Schwob, H. Otto, Sadia Bari, Zheng Li, V. Zhaunerchyk, Timur Osipov, Patrik Grychtol, Mehdi Mohammad Kazemi, Robert Mason, Arno Ehresmann, Simon Dörner, Rebecca Boll, C. von Korff Schmising, Günter Brenner, Markus Ilchen, Ph V. Demekhin, Andreas Galler, Rene Wagner, Felix Allum, Ludger Inhester, V. Music, Benjamin Erk, David Heathcote, Jongmin Lee, Kaja Schubert, Christopher Passow, R. Thomas, T. M. Baumann, Patrick Rupprecht, Michael Meyer, Stefan Moeller, Peter Walter, L. Marder, Ph. Schmidt, Thomas Wolf, Daniel Rolles, Bastian Manschwetus, and André Knie

Subjects
Free electron model, History, Materials science, Physics::Instrumentation and Detectors, Physics::Optics, Laser, Computer Science Applications, Education, law.invention, Chemical physics, law, Physics::Atomic and Molecular Clusters, ddc:530, Physics::Atomic Physics, Physics::Chemical Physics, Ultrashort pulse
Abstract

31st International Conference on Photonic, Electronic, and Atomic Collisions, ICPEAC XXXI, Caen Normandy, France, 23 Jan 2019 - 30 Jan 2019; Journal of physics / Conference Series 1412, 112009 (2020). doi:10.1088/1742-6596/1412/11/112009, (X-ray) free-electron lasers are employed to site specifically interrogate atomic fragments during ultra-fast photolysis of chiral molecules via time-resolved photoelectron circular dichroism., Published by IOP Publ., Bristol

Published
2020
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25. Coulomb explosion imaging of CH

Author

Felix, Allum, Michael, Burt, Kasra, Amini, Rebecca, Boll, Hansjochen, Köckert, Pavel K, Olshin, Sadia, Bari, Cédric, Bomme, Felix, Brauße, Barbara, Cunha de Miranda, Stefan, Düsterer, Benjamin, Erk, Marie, Géléoc, Romain, Geneaux, Alexander S, Gentleman, Gildas, Goldsztejn, Renaud, Guillemin, David M P, Holland, Iyas, Ismail, Per, Johnsson, Loïc, Journel, Jochen, Küpper, Jan, Lahl, Jason W L, Lee, Sylvain, Maclot, Stuart R, Mackenzie, Bastian, Manschwetus, Andrey S, Mereshchenko, Robert, Mason, Jérôme, Palaudoux, Maria Novella, Piancastelli, Francis, Penent, Dimitrios, Rompotis, Arnaud, Rouzée, Thierry, Ruchon, Artem, Rudenko, Evgeny, Savelyev, Marc, Simon, Nora, Schirmel, Henrik, Stapelfeldt, Simone, Techert, Oksana, Travnikova, Sebastian, Trippel, Jonathan G, Underwood, Claire, Vallance, Joss, Wiese, Farzaneh, Ziaee, Mark, Brouard, Tatiana, Marchenko, and Daniel, Rolles

Abstract

The photodissociation dynamics of CH

Published
2018

26. Ultrafast ionization and fragmentation dynamics of polycyclic atomatic hydro-carbons by XUV radiation

Author

Simon Dörner, X. Cheng, Bastian Manschwetus, Nora Schirmel, Sébastien Gruet, Amanda L. Steber, Anouk M. Rijs, Farzaneh Ziaee, Benjamin Erk, Jochen Küpper, Rebecca Boll, Jan Lahl, C. Vallence, Sebastian Trippel, Mehdi Mohammad Kazemi, Denis S. Tikhonov, Pragya Chopra, Felix Allum, Michael Burt, Robert Mason, Jongmin Lee, Christopher Passow, Hansjochen Köckert, T. Mullins, Pavel K. Olshin, Sadia Bari, Daniel Rolles, Daniel Ramm, Melby Johny, Per Johnsson, Jasper Peschel, Erland Müller, Mark Brouard, Joss Wiese, David Heathcote, Melanie Schnell, Dimitrios Rompotis, Sylvain Maclot, Alexander K. Lemmens, and Lanhai He

Subjects
FELIX Molecular Structure and Dynamics, chemistry.chemical_classification, History, Materials science, Double ionization, Polycyclic aromatic hydrocarbon, Phenanthrene, Fluorene, Photochemistry, Hydrogen atom abstraction, Computer Science Applications, Education, chemistry.chemical_compound, chemistry, Extreme ultraviolet, Ionization, Pyrene
Abstract

Synopsis In the interstellar medium polycyclic aromatic hydrocarbon molecules (PAH) are exposed to strong ionizing radation leading to complex organic photochemistry. We investigated these ultrafast fragmentation reactions after ionization of the PAHs phenanthrene, fluorene and pyrene at a wavelength of 30.3 nm using pump probe spectroscopy at a free electron laser. We observe double ionization and afterwards hydrogen abstraction and acetylene loss with characteristic time scales for the reaction processes below one hundred femtoseconds.

Published
2020
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27. Coulomb explosion imaging of CH3I and CH2CII photodissociation dynamics

Author

Barbara Cunha de Miranda, Per Johnsson, Romain Géneaux, Stuart R. Mackenzie, I. Ismail, Hansjochen Köckert, David M. P. Holland, Dimitrios Rompotis, Marie Géléoc, Jérôme Palaudoux, Loic Journel, Jonathan G. Underwood, Farzaneh Ziaee, Jan Lahl, Robert Mason, Kasra Amini, Mark Brouard, Gildas Goldsztejn, Artem Rudenko, Stefan Düsterer, Sylvain Maclot, Maria Novella Piancastelli, Arnaud Rouzée, Thierry Ruchon, Daniel Rolles, Michael Burt, Jongmin Lee, Rebecca Boll, Oksana Travnikova, Andrey S. Mereshchenko, Joss Wiese, Sebastian Trippel, Marc Simon, Francis Penent, Felix Allum, Felix Brauße, Bastian Manschwetus, Simone Techert, Evgeny Savelyev, Tatiana Marchenko, Henrik Stapelfeldt, Renaud Guillemin, Nora Schirmel, Cédric Bomme, Benjamin Erk, Alexander S. Gentleman, Claire Vallance, Pavel K. Olshin, Sadia Bari, Jochen Küpper, University of Oxford, Deutsches Elektronen-Synchrotron [Hamburg] (DESY), Saint Petersburg State Polytechnical University (SPSPU), KVI Atomic and Molecular Physics (KVI), University of Groningen [Groningen], Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), Laboratoire Interactions, Dynamiques et Lasers (ex SPAM) (LIDyl), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Attophysique (ATTO), Institut Rayonnement Matière de Saclay (IRAMIS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Laboratoire Interactions, Dynamiques et Lasers (ex SPAM) (LIDyl), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Chimie Physique - Matière et Rayonnement (LCPMR), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Microbiology Laboratory, Middlemore Hospital, Laboratoire des collisions atomiques et moléculaires (LCAM), Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Department of Physics, Lund Institute of Technology, Lund University [Lund]-Lund University [Lund], Lund University [Lund], Centre de recherche sur les Ions, les MAtériaux et la Photonique (CIMAP - UMR 6252), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-École Nationale Supérieure d'Ingénieurs de Caen (ENSICAEN), Normandie Université (NU)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche sur les Matériaux Avancés (IRMA), Normandie Université (NU)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU)-Institut national des sciences appliquées Rouen Normandie (INSA Rouen Normandie), Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Rouen Normandie (UNIROUEN), Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS), Physical and Theoretical Chemistry Laboratory, Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Interdisciplinaire Carnot de Bourgogne (ICB), Université de Bourgogne (UB)-Centre National de la Recherche Scientifique (CNRS), Kansas State University, Georg-August-University = Georg-August-Universität Göttingen, Department of Physics and Astronomy [UCL London], University College of London [London] (UCL), Center for Free-Electron Laser Science (CFEL), ANR-16-CE30-0001,ATTOMEMUCHO,Dynamique électronique attoseconde dans les molécules organiques isolées par la spectroscopie 'core-hole clock'(2016), University of Oxford [Oxford], Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Normandie Université (NU)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Interdisciplinaire Carnot de Bourgogne (LICB), Georg-August-University [Göttingen], Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Ingénieurs de Caen (ENSICAEN), Normandie Université (NU)-Normandie Université (NU)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Caen Normandie (UNICAEN), and Normandie Université (NU)

Subjects
Atom and Molecular Physics and Optics, Imaging spectrometer, General Physics and Astronomy, 02 engineering and technology, Physical Chemistry, 01 natural sciences, Molecular physics, Mass spectrometry imaging, Ion, 0103 physical sciences, Molecule, ddc:530, Physical and Theoretical Chemistry, 010306 general physics, ComputingMilieux_MISCELLANEOUS, Fysikalisk kemi, Physics, Coupling, Range (particle radiation), Photodissociation, Coulomb explosion, 021001 nanoscience & nanotechnology, 3. Good health, Atom- och molekylfysik och optik, [PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph], 0210 nano-technology
Abstract

The journal of chemical physics 149(20), 204313 (2018). doi:10.1063/1.5041381, The photodissociation dynamics of CH$_3$I and CH$_2$ClI at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815 nm probe pulse. Fragment ion momenta over a wide m/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH$_2$ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion., Published by American Institute of Physics, Melville, NY

Published
2018
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