Decay of and OCS after sulphur 1s photoexcitation: II. Dissociation channels and kinematics

Abstract

CS 2 and OCS molecules were excited and fragmented by x-rays of variable energy around the sulphur 1s threshold (2478 eV). Coincident detection of three ionic fragments by a time-of-flight mass spectrometer enabled the determination of branching ratios for 18 dissociation channels with total ionic charges between 2 and 7. While the electronic de-excitation is similar in both molecules (see the preceding paper), the dissociation shows differences, notably a more asymmetric distribution of charge onto the fragments of OCS. Branching among channels of the same total charge is independent of photon energy although the dominant de-excitation cascades are not. This is interpreted as an indication of strong interchannel mixing. A simple, parameter-free Coulomb explosion model to simulate the dissociative kinematics is described. Detailed results based on this model give, contrary to opinions to be found in the literature, very good agreement with observed momentum correlations whereas maximum kinetic energies are somewhat overestimated for channels of higher total charge.

Ultrafast Charge Rearrangement and Nuclear Dynamics upon Inner-Shell Multiple Ionization of Small Polyatomic Molecules

“…Low charge states are predominantly produced by single photon absorption, such that fast dissociation starts upon ultrafast core-vacancy decay resulting in kinetic energies of the heavy ions that are in reasonable agreement with the simulations for equilibrium geometry. This is in line with the outcome of earlier synchrotron experiment for the case of S (1s) ionization of OCS molecules [23]. In contrast, the lightest ionic fragmentsprotons-are considerably displaced even within this very short time (in 1 fs a proton with one atomic unit of energy (27.2 eV) moves about 3.5 Å , i.e., more than a bond length per fs).…”

Selecting core-hole localization or delocalization in CS2 by photofragmentation dynamics

“…The binding energy of the S 1s core electrons in CS 2 is 2,478 eV (ref. 18). Core ionization leaves the system in a highly unstable state that decays either through photon emission or Auger decay, the latter being the dominant channel (B90%).…”

“…Core ionization leaves the system in a highly unstable state that decays either through photon emission or Auger decay, the latter being the dominant channel (B90%). After deep-core ionization, relaxation processes often occur in a cascade involving multiple Auger decays, several electrons are emitted sequentially, and highly charged ions are produced [18][19][20] . When a molecule containing only a few atoms is multiply ionized and left in a charge state in which each constituent atom can carry positive charge, it primarily dissociates through Coulomb repulsion.…”

“….6% of all fragments) 18,21,22 . As it turns out, following the path from ionization of a S 1s core electron in CS 2 to the production of two distinguishable sulfur ions, S þ and S 2 þ provides an ideal experimental scheme to study core-hole localization versus delocalization.…”

Evidence for interatomic Coulombic decay in XeK-shell-vacancy decay of XeF2

“…The common hypothesis for deep inner-shell decay in a molecular environment is that of a localized cascade decay on the heavy atom accompanied by charge redistribution and Coulomb explosion [1,2,9,10]. Within this scenario, the same total final charge is produced in the cascade decay of an isolated heavy atom and in the decay of the same atom embedded in an environment.…”