Ab initio multichannel calculation of the Bethe surface and Compton defects for molecular hydrogen

Abstract

A correlated multichannel computation of the generalized oscillator-strength density for electrons scattering off randomly oriented molecular hydrogen at the internuclear separation of 1.4 $a_0$ is being presented. The numerical procedure features a novel free-boundary method based on configuration interaction of ionic orbitals expanded in B splines using prolate-spheroidal coordinates. Satisfactory agreement between the present and both experimental as well as other theoretical results has been found, thus providing a view on the Bethe surface for energy transfers up to of 558 eV. The systematic and robust convergence behavior of the method further allowed for assessing the validity of the binary-encounter approximation, providing a confirmation of experimentally determined Compton defects for H$_2$ using a single consistent theoretical description. Overall, the present findings are expected to be helpful for calculating highly accurate energy-loss spectra for fast electrons passing through and ionizing molecular hydrogen gas or its isotopologues.