Angle resolved photoelectron spectroscopy of O2(a1Δg) with synchrotron radiation

Abstract

Angular distribution of photoelectrons for the photoionization processes O2+(X 2Πg,v+=0–3)+e−←O2(a1Δg)+hν has been studied at the photon energy of 21.22 eV and in the photon energy range 13.8–15.2 eV where the cross-sections for these processes show strong enhancement due to the presence of resonant transitions to a Rydberg state (C 2Φu,3sσg)p 1Φu. It has been found that the plot of the asymmetry parameter, β, against photon energy shows structure at energies corresponding to O2(p 1Φuv′)←O2(a 1Δgv″=0) excitations. The O2+(X 2Πg,v+)←O2(a 1Δg,v″=0) ionizations have also been investigated in the photon energy range 18.0–19.2 eV, where the presence of unassigned resonances was observed in earlier photoelectron spectroscopic work. In this energy range the plot of asymmetry parameter against photon energy also shows resonant structure. Suggestions for the excited states associated with these resonances have been made on the basis of constant-ionic-state spectra recorded at different angles.