Electronic-state interference in the C 1s excitation and decay of methyl chloride studied by angularly resolved Auger spectroscopy

Abstract

Resonant Auger (RA) decay spectra of carbon $1s$ excited ${\mathrm{CH}}_{3}\mathrm{Cl}$ molecules are recorded with angular resolution using linearly polarized synchrotron radiation. The selected photon energies corresponding to the C $1s\ensuremath{\rightarrow}8{a}_{1}$ core to lowest unoccupied molecular orbital and C $1s\ensuremath{\rightarrow}4s{a}_{1}$, $4pe$, and $4p{a}_{1}$ core to Rydberg excitations of methyl chloride are used and electrons in the binding energy range of 11--37 eV are detected. The vibrationally unresolved RA electron angular distributions, recorded for participator Auger transitions populating the $X$, $A$, $B$, and $C$ states of the ${\mathrm{CH}}_{3}{\mathrm{Cl}}^{+}$ ion, exhibit strong variations across the selected electronic resonances. These observations are interpreted with the help of ab initio electronic structure and dynamics calculations, which account for electronic-state interference between the direct and different resonant ionization pathways. For spectator transitions, the theory predicts almost isotropic angular distributions with moderate changes of $\ensuremath{\beta}$ parameters around zero, which is in agreement with the experimental observations.