Vibrational averaging effects on the valence-shell electron momentum distributions in H 2O employing Hartree-Fock-limit wavefunctions

Abstract

Vibrational averaging effects on electron momentum distributions in the valence shell of H 2O are calculated employing Hartree-Fock-limit electronic wavefunctions and an accurate empirical ground-state potential energy surface. The effects are generally small, lending support to the widespread practice of evaluating theoretical electron momentum distributions at fixed equilibrium geometries, in accordance with summations over unresolved final vibrational states in the vertical electronic Franck-Condon approximation. Vibrational corrections to the angle-averaged 3a 1 and 1b 2 orbital momentum distributions in H 2O, slightly reduce existing discrepancies between calculations and previously reported (e, 2e) experiments for small values of target electron momentum. This suggests that vibrational averaging should generally be incorporated in refined computational studies of electron momentum distributions in polyatomic molecules, and should be combined with the generally more significant effects of finite experimental momentum resolution when comparisons are made with measured values derived from (e, 2e) spectroscopy.