Photoexcited K Auger spectra of atomic and molecular oxygen

Abstract

K Auger spectra of the oxygen atom following either 1s photoionization or 1s → np photoexcitation are presented and compared with energy and transition rate calculations where available. Data are juxtaposed to earlier results on neon, showing that the excellent agreement between theory and experiment which exists for the closed-shell atom neon does not, at present, extend to the open-shell atom oxygen. Auger spectra following 1s → 2p excitation in the O atom and 1s, 2p double ionization in Ne are found to have similar branching ratios. All major lines in the Auger spectra of oxygen could be resolved and fully analyzed with regard to energies, branching ratios, and angular distributions. A strong anisotropy is measured for the Auger transitions associated with the 1s → 2p excitation. The 1σ u → 1π g and 1σ g → 3σ u resonance Auger spectra of molecular oxygen are also presented. The angular distributions of the high kinetic energy lines in the molecular spectra are measured, and the atomic-like Auger lines in the 3σ u decay are compared with the pure atomic 2p decay spectrum. Energies of the Kα X-ray transitions in the atom are deduced. The experimental setup, which allowed us to record these low- Z atomic Auger spectra for the first time, is described in some detail.