Resonant excitation and decay of core holes in condensed layers of furan and pyrrole

Abstract

Near edge x-ray absorption spectra and decay electron spectra for resonant and nonresonant excitations in the C 1s and N 1s regions have been measured for condensed furan (C4H4O) and pyrrole (C4H4NH) layers. The decay spectra after resonant excitation into the lowest unoccupied orbital (π*4) are pure autoionization spectra. The participant channels show strong resonant enhancements of the photoelectron peaks, in particular after excitation of the C 1s core electrons. Overall however, the spectra are dominated by the spectator channels. The spectator spectra resemble the normal Auger spectra shifted by spectator shifts of ≊4 eV for furan and ≊2.5 eV for pyrrole. For furan the participant spectra for excitation at the two different carbon atoms show significant differences that can be qualitatively understood in terms of a simple one-electron picture by considering the localization of the corresponding orbitals on the core hole. The decay spectra after excitation into the π*5 orbital show negligible enhancement of the participant channel, a strongly reduced spectator shift, and less-pronounced structures than at higher photon energies. The latter is attributed to a competition of spectator decay and normal Auger decay after internal photoionization into Rydberg derived bands in the condensate. For excitations into the σ*-resonances pure Auger spectra are observed, indicating that these resonances fully ionize before core decay takes place.