(E,2E) MOMENTUM SPECTROSCOPIC STUDY OF THE VALENCE ORBITALS OF HYDROGEN SELENIDE

Electron momentum densities of the four valence molecular orbitals of H2Se have been measured by (e, 2e) spectroscopy. Although the three ou termost orbitals all show momentum densities that are qualitatively si milar to the 4p orbital of a free Se atom, a detailed comparison of th e orbital momentum densities using the autocorrelation function approa ch reveals differences consistent with the usual qualitative molecular orbital (MO) theoretical representations of these orbitals. For H2Se, as for H2S previously studied by others, the experimental (e, 2e) mom entum densities are accurately described by near-Hartree-Fock level or bital 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 H2Se. This is in cont rast to H2O where such effects are substantial, particularly for the h ighest-occupied molecular orbital (HOMO).