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

ABSTRACT: Inner-shell photoelectron spectroscopy provides an element-specific probe of molecular structure, as core-electron binding energies are sensitive to the chemical environment. Short-wavelength femtosecond light sources, such as Free-Electron Lasers (FELs), even enable time-resolved site-specific investigations of molecular photochemistry. Here, we study the ultraviolet photodissociation of the prototypical chiral molecule 1-iodo-2-methylbutane, probed by extreme-ultraviolet (XUV) pulses from the Free-electron LASer in Hamburg (FLASH) through the ultrafast evolution of the iodine 4d binding energy. Methodologically, we employ electron-ion partial covariance imaging as a technique to isolate otherwise elusive features in a two-dimensional photoelectron spectrum arising from different photofragmentation pathways. The experimental and theoretical results for the time-resolved electron spectra of the 4d_3/2 and 4d_5/2 atomic and molecular levels that are disentangled by this method provide a key step towards studying structural and chemical changes from a specific spectator site.

SUBMITTER: Allum F

PROVIDER: S-EPMC9814695 | biostudies-literature | 2022 Mar

REPOSITORIES: biostudies-literature

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

Allum Felix F Music Valerija V Inhester Ludger L Boll Rebecca R Erk Benjamin B Schmidt Philipp P Baumann Thomas M TM Brenner Günter G Burt Michael M Demekhin Philipp V PV Dörner Simon S Ehresmann Arno A Galler Andreas A Grychtol Patrik P Heathcote David D Kargin Denis D Larsson Mats M Lee Jason W L JWL Li Zheng Z Li Zheng Z Manschwetus Bastian B Marder Lutz L Mason Robert R Meyer Michael M Otto Huda H Passow Christopher C Pietschnig Rudolf R Ramm Daniel D Schubert Kaja K Schwob Lucas L Thomas Richard D RD Vallance Claire C Vidanović Igor I von Korff Schmising Clemens C Wagner René R Walter Peter P Zhaunerchyk Vitali V Rolles Daniel D Bari Sadia S Brouard Mark M Ilchen Markus M

Communications chemistry 20220328 1

Inner-shell photoelectron spectroscopy provides an element-specific probe of molecular structure, as core-electron binding energies are sensitive to the chemical environment. Short-wavelength femtosecond light sources, such as Free-Electron Lasers (FELs), even enable time-resolved site-specific investigations of molecular photochemistry. Here, we study the ultraviolet photodissociation of the prototypical chiral molecule 1-iodo-2-methylbutane, probed by extreme-ultraviolet (XUV) pulses from the ...[more]

PMID: 36697752

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Project description:Hydrated divalent magnesium and calcium clusters are used as nanocalorimeters to measure the internal energy deposited into size-selected clusters upon capture of a thermally generated electron. The infrared radiation emitted from the cell and vacuum chamber surfaces as well as from the heated cathode results in some activation of these clusters, but this activation is minimal. No measurable excitation due to inelastic collisions occurs with the low-energy electrons used under these conditions. Two different dissociation pathways are observed for the divalent clusters that capture an electron: loss of water molecules (Pathway I) and loss of an H atom and water molecules (Pathway II). For Ca(H(2)O)(n)(2+), Pathway I occurs exclusively for n >or= 30 whereas Pathway II occurs exclusively for n <or= 22 with a sharp transition in the branching ratio for these two processes that occurs for n approximately 24. The number of water molecules lost by both pathways increases with increasing cluster size reaching a broad maximum between n = 23 and 32, and then decreases for larger clusters. From the number of water molecules that are lost from the reduced cluster, the average and maximum possible internal energy is determined to be approximately 4.4 and 5.2 eV, respectively, for Ca(H(2)O)(30)(2+). This value is approximately the same as the calculated ionization energies of M(H(2)O)(n)(+), M = Mg and Ca, for large n indicating that the vast majority of the recombination energy is partitioned into internal modes of the ion and that the dissociation of these ions is statistical. For smaller clusters, estimates of the dissociation energies for the loss of H and of water molecules are obtained from theory. For Mg(H(2)O)(n)(2+), n = 4-6, the average internal energy deposition is estimated to be 4.2-4.6 eV. The maximum possible energy deposited into the n = 5 cluster is <7.1 eV, which is significantly less than the calculated recombination energy for this cluster. There does not appear to be a significant trend in the internal energy deposition with cluster size whereas the recombination energy is calculated to increase significantly for clusters with fewer than 10 water molecules. These, and other results, indicate that the dissociation of these smaller clusters is nonergodic.

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

Publications

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

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