Theoretical studies in photoelectron spectroscopy: Use of angular distribution data to deduce molecular orobital parameters. IV. Calculation of angular distributions for ejection of low-energy photoelectrons from molecules having 1sσ2g, 2pσ2g, or 2pσ2u configurations

Abstract

Angular distributions are calculated for the ejection of photoelectrons in the energy range of less than 1 eV to above 50 eV from molecules having 1sσ2g, 2pσ2g, or 2pσ2u configurations. The continuum wavefunction for the photoelectron is calculated in the ’’static-exchange’’ approximation of electron–molecular ion scattering theory by numerical integration of the one-electron integrodifferential equations appropriate for this approximation, accounting accurately for screening and exchange effects in the photoelectron–molecular ionic system. These equations are coupled in the radial partial waves relative to the center of mass of the nuclei, and they are solved both for the case of complete uncoupling and for the cases of coupled s and d waves, for ejection from a 2pσu molecular orbital, and of coupled p and f waves, for ejection from a 1sσg or 2pσg molecular orbital. Formulas are presented for the asymmetry parameter β for each of these cases. Provided enough data are available it may be possible to use these formulas to interpret experimental results in the absence of calculations. We study partial wave coupling in the photoelectron–molecular ionic motion. It is found that a molecular ionic core in the 1sσg state provides a field in which the coupling between partial waves is weak, even at fairly large internuclear distances. A core in the 2pσg state provides a field in which the coupling is weak to moderate, and a core in the 2pσu state provides a field in which the coupling is moderate to strong as a function of energy and internuclear distance. The possibility of the interpretation of the over-all qualitative features of angular distributions for many-electron molecules in terms of a paradigm of results for photoionization of a molecule with a filled nlσi shell is discussed with reference to experimental results for N2, and it is proposed that the effective charge parameter of the molecular orbitals belonging to the neutral and ionic systems and the bare nuclear charge could be treated as adjustable parameters to provide a crude but qualitatively correct description of the screening in the many-electron molecule.