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Ho PJ, Ray D, Lehmann CS, Fouda AEA, Dunford RW, Kanter EP, Doumy G, Young L, Walko DA, Zheng X, Cheng L, Southworth SH. X-ray induced electron and ion fragmentation dynamics in IBr. J Chem Phys 2023; 158:134304. [PMID: 37031139 DOI: 10.1063/5.0145215] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/07/2023] Open
Abstract
Characterization of the inner-shell decay processes in molecules containing heavy elements is key to understanding x-ray damage of molecules and materials and for medical applications with Auger-electron-emitting radionuclides. The 1s hole states of heavy atoms can be produced by absorption of tunable x rays and the resulting vacancy decays characterized by recording emitted photons, electrons, and ions. The 1s hole states in heavy elements have large x-ray fluorescence yields that transfer the hole to intermediate electron shells that then decay by sequential Auger-electron transitions that increase the ion’s charge state until the final state is reached. In molecules, the charge is spread across the atomic sites, resulting in dissociation to energetic atomic ions. We have used x-ray/ion coincidence spectroscopy to measure charge states and energies of I q+ and Br q′+ atomic ions following 1s ionization at the I and Br K-edges of IBr. We present the charge states and kinetic energies of the two correlated fragment ions associated with core-excited states produced during the various steps of the cascades. To understand the dynamics leading to the ion data, we develop a computational model that combines Monte-Carlo/Molecular-Dynamics (MC/MD) simulations with a classical over-the-barrier model to track inner-shell cascades and redistribution of electrons in valence orbitals and nuclear motion of fragments.
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Affiliation(s)
- Phay J. Ho
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Dipanwita Ray
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - C. Stefan Lehmann
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Adam E. A. Fouda
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Robert W. Dunford
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Elliot P. Kanter
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Gilles Doumy
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Linda Young
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
- The James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Donald A. Walko
- Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, USA
| | - Xuechen Zheng
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Lan Cheng
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Stephen H. Southworth
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, USA
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Das R, Pandey DK, Soumyashree S, P M, Nimma V, Bhardwaj P, K M MS, Singh DK, Kushawaha RK. Strong-field ionization of CH 3Cl: proton migration and association. Phys Chem Chem Phys 2022; 24:18306-18320. [PMID: 35880610 DOI: 10.1039/d2cp02494b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Strong-field ionization of CH3Cl using femtosecond laser pulses, and the subsequent two-body dissociation of CH3Cl2+ along Hn+ (n = 1-3) and HCl+ forming pathways, have been experimentally studied in a home-built COLTRIMS (cold target recoil ion momentum spectrometer) setup. The single ionization rate of CH3Cl was obtained experimentally by varying the laser intensity from 1.6 × 1013 W cm-2 to 2.4 × 1014 W cm-2 and fitted with the rate obtained using the MO-ADK model. Additionally, the yield of Hn+ ions resulting from the dissociation of all charge states of CH3Cl was determined as a function of intensity and pulse duration (and chirp). Next, we identified four two-body breakup pathways of CH3Cl2+, which are H+ + CH2Cl+, H2+ + CHCl+, H3+ + CCl+, and CH2+ + HCl+, using photoion-photoion coincidence. The yields of the four pathways were found to decrease on increasing the intensity from I = 4.2 × 1013 W cm-2 to 2I = 8.5 × 1013 W cm-2, which was attributed to enhanced ionization of the dication before it can dissociate. As a function of pulse duration (and chirp), the Hn+ forming pathways were suppressed, while the HCl+ forming pathway was enhanced. To understand the excited state dynamics of the CH3Cl dication, which controls the outcome of dissociation, we obtained the total kinetic energy release distributions of the pathways and the two-dimensional coincidence momentum images and angular distributions of the fragments. We inferred that the Hn+ forming pathways originate from the dissociation of CH3Cl dications from weakly attractive metastable excited states having a long dissociation time, while for the HCl+ forming pathway, the dication dissociates from repulsive states and therefore, undergoes rapid dissociation. Finally, quantum chemical calculations have been performed to understand the intramolecular proton migration and dissociation of the CH3Cl dication along the pathways mentioned above. Our study explains the mechanism of Hn+ and HCl+ formation and confirms that intensity and pulse duration can serve as parameters to influence the excited state dynamics and hence, the outcome of the two-body dissociation of CH3Cl2+.
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Affiliation(s)
- Rituparna Das
- Physical Research Laboratory Ahmedabad, Gujarat 380009, India.
| | - Deepak K Pandey
- Department of Basic Sciences, Institute of Infrastructure Technology Research And Management, Ahmedabad-380026, India.
| | | | - Madhusudhan P
- Physical Research Laboratory Ahmedabad, Gujarat 380009, India.
| | - Vinitha Nimma
- Physical Research Laboratory Ahmedabad, Gujarat 380009, India.
| | - Pranav Bhardwaj
- Physical Research Laboratory Ahmedabad, Gujarat 380009, India.
| | | | - Dheeraj K Singh
- Department of Basic Sciences, Institute of Infrastructure Technology Research And Management, Ahmedabad-380026, India.
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