Shape resonances and multielectron effects in the core-level photoionization of CO2.

Abstract

The partial photoionization cross sections and angular distributions of the C 1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$ and O 1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$ single-hole states of ${\mathrm{CO}}_{2}$ have been measured with high precision near threshold. The 4${\mathrm{\ensuremath{\sigma}}}_{\mathit{u}}^{\mathrm{*}}$ shape resonance is well reproduced in the 1s single-hole cross sections, but strong site-specific effects are observed with respect to both its energy and intensity. A striking feature of the present data is the presence of fine structure in the 1s single-hole cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{SH}}$ due to multielectron excitations: virtually all spectral details in the total 1s cross sections ${\mathrm{\ensuremath{\sigma}}}_{1\mathit{s}}$ are also present in ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{SH}}$ implying that multielectron excitations couple strongly to the underlying 1s continuum. The decay dynamics of the double-excitation feature at 303.5 eV in the C 1s cross section of ${\mathrm{CO}}_{2}$ have been characterized by Auger spectroscopy. Partial cross sections and angular distributions have also been measured for the first group of strong shake-up satellites in the C 1s photoelectron spectrum. Similar to the C 1s ionization of CO, a strong enhancement of intensity near threshold is observed for some satellite channels as well as the occurrence of features that are not present in the sudden limit. The latter are attributed to conjugate shake-up.