Theoretical studies of partial-channel photoionization cross sections in diatomic and polyatomic molecules

Abstract

An account is given of recent theoretical studies of partial-channel photoionization cross sections in diatomic and polyatomic molecules employing separated-channel static-exchange calculations and Stieltjes-Tchebycheff moment-theory techniques. The calculated cross sections, which refer to production of specific parent molecular-ionic states upon removal of electrons from individual orbitals, are compared with the results of photoabsorption, electron-impact-excitation, fluorescence-production, photoelectron spectroscopy, and dipole (e, 2e) measurements. Various structures in the calculated and measured partial-channel cross sections as functions of incident photon energy are identified as having either atomiclike or molecularlike origins. Specifically, σ-orbital cross sections in light diatomic and polyatomic molecules are found to be generally dominated by strong σ - σ^* photoionization resonances of molecularlike origin, whereas π-Orbital cross sections in such molecules exhibit distinctly 2p → kd atomiclike features. These aspects of molecular photoionization are illustrated by detailed theoretical studies of partial-channel cross sections in CO, C0_2, and H_2CO, the results of which are in generally good accord with corresponding measured values.