Autoionization of OCS by threshold photoelectron spectroscopy

Abstract

Autoionization of carbonyl sulfide between 12 and 16 eV has been investigated by photoionization using the pulsed synchrotron radiation from ACO Orsay’s storage ring. The threshold photoelectron spectrum and the total photoionization spectrum of carbonyl sulfide have been recorded at high resolution in the wavelength range between 112.0 and 65.0 nm (11–19 eV). Threshold energy electrons are observed in specific wavelength regions: (i) at excitation energies where the X̃, Ã, B̃, and C̃ ionic states are formed by a direct process; (ii) in the à state region where resonant autoionization to à can be understood classically within the Franck–Condon approximation; (iii) in the ÖX̃ Franck–Condon gap between 90 and 110 nm, where resonant autoionization leads to very sharp electron energy distribution strongly peaked at zero energy. Here the mechanism must be more complex.