Rotationally resolved photoionization of molecular oxygen

Abstract

We report the results of theoretical studies of the rotationally resolved photoelectron spectra of ground state O_2 leading to the X ^2Π_g state of O^+ 2 via the absorption of a single vacuum ultraviolet photon. These studies elaborate on a recent report [M. Braunstein e t a l., J. Chem. Phys. 9 3, 5345 (1990)] where we showed that a shape resonance near threshold creates a significant dependence of the rotational branching ratios on the ion vibrational level. We also showed that analysis of the rotational branches yields detailed information on the angular momentum composition of the shape resonance. We continue this analysis giving a comprehensive derivation of the rotationally resolved cross sections and photoelectron angular distributions. We discuss the selection rules implied by these expressions and present very high resolution cross sections (J→J^+) obtained using static‐exchange photoelectron orbitals and explicitly taking into account the internuclear distance dependence of the electronic transition moment. These cross sections illustrate the selection rules and show more explicitly the angular momentum composition of the shape resonance. We also present rotationally resolved photoelectron angular distributions which would be expected at low energy.