Photoabsorption, photoionization, and Auger processes at the carbonKedge inCH3I

Abstract

The dynamics of photoabsorption, photoionization, and the associated Auger decay have been investigated at the carbon $K$ edge in methyl iodide ($\mathrm{C}{\mathrm{H}}_{3}\mathrm{I}$) using linearly polarized synchrotron radiation. Ion yield measurements were used to investigate transitions in the pre-edge region due to excitations into either unoccupied valence or Rydberg states. The assignment of these transitions was achieved through comparison with theoretical x-ray absorption spectra calculated using time-dependent density functional theory, within the Tamm-Dancoff approximation. Several of the Rydberg states belonging to series converging onto the $\mathrm{C}1s$ ionization limit exhibit significant vibrational structure that is also interpreted using theoretical calculations. The $\mathrm{C}1s$ in $\mathrm{C}{\mathrm{H}}_{3}\mathrm{I}$ photoelectron spectrum was measured, and the observed vibrational structure was assigned with the aid of theoretical predictions. Polarization dependent, resonantly excited, valence shell photoelectron spectra were recorded at photon energies coinciding with the $\mathrm{C}\phantom{\rule{0.16em}{0ex}}1s\ensuremath{\rightarrow}{\ensuremath{\sigma}}^{*}, \mathrm{C}\phantom{\rule{0.16em}{0ex}}1s\ensuremath{\rightarrow}6s{a}_{1}$ and $\mathrm{C}\phantom{\rule{0.16em}{0ex}}1s\ensuremath{\rightarrow}6pe$ transitions in $\mathrm{C}{\mathrm{H}}_{3}\mathrm{I}$, thereby allowing photoelectron angular distributions to be determined. The nonresonantly excited C(KVV) Auger electron spectrum was measured and some of the features observed at high kinetic energies were attributed to transitions into valence orbitals possessing significant iodine character. The contributions of participator and spectator Auger decay to the resonantly excited photoelectron spectra have been assessed. The influence of participator decay appears minor whereas spectator decay results in the enhanced population of satellite states.