Angular distribution and intensity in molecular photoelectron spectroscopy I. General theory for diatomic molecules

Abstract

Molecular photoelectron spectroscopy has become a source of extensive data on molecular ionization potentials, orbital energies, and Franck–Condon factors in ionization. Also, Berry (1966) suggested that a study of the angular distribution of photoelectrons might be useful in determining those photon energies at which autoionization is important if the angular distribution of autoionized electrons is different from that for directly ionized electrons. Experiments on the angular distribution of photoelectrons ejected from molecules suggest that the angular distribution may be useful as a source of information about the symmetry of the molecular orbital from which the photoelectrons of a given energy are ejected. This chapter discusses a theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules. The theory treats molecular rotation explicitly, so that it is applicable to the transitions between individual rotational levels; different angular distributions are found according to whether rotational structure is resolved or not. Detailed calculations to determine the important contributions to the anisotropy parameter for the orbitals of various symmetries are in progress.