(e, 2e) Momentum spectroscopic study of the valence orbitals of hydrogen selenide

Abstract

Electron momentum densities of the four valence molecular orbitals of H 2Se have been measured by (e, 2e) spectroscopy. Although the three outermost orbitals all show momentum densities that are qualitatively similar to the 4p orbital of a free Se atom, a detailed comparison of the orbital momentum densities using the autocorrelation function approach reveals differences consistent with the usual qualitative molecular orbital (MO) theoretical representations of these orbitals. For H 2Se, as for H 2S previously studied by others, the experimental (e,2e) momentum densities are accurately described by near-Hartree-Fock level orbital momentum density calculations. Results from direct calculations of the SCF-CI overlap densities and the SCF orbital momentum densities with a 3-21G * basis are found to be very similar. This suggests that relaxation and correlation effects are small for H 2Se. This is contrast to H 2O where such effects are substantial, particularly for the highest-occupied molecular orbital (HOMO).