Angle-differential electron energy spectra for the autoionization systems He∗ (2 1S) + H/D(1 2S): Comparison between ab initio theory and experiment

Abstract

We present angle-dependent electron energy spectra due to ionizing collisions ofmetastable He∗ (2 1S) atoms with ground-state hydrogen and deuterium atoms. The data, measured at thermal collision energies (Ērel≈50 meV), show an angular variation of the spectral shape which is well reproduced by a quantum-mechanical calculation based on local complex potential theory. The ab initio calculated resonance-to-continuum complex coupling elements show a strong dependence on the electronic structure of the quasi-molecule and its changes with internuclear separation. Therefore the total autoionization width shows a significant deviation from a damped exponential shape. Autoionization occurs dominantly into the (molecule fixed) electronic p wave. Calculated total autoionization cross sections are 84 Å2 at Erel = 50 meV. and follow approximately a Erel−0.5 decay for larger energies. At Erel = 50 meV, associative and quasi-associative processes account for about 12% and 4%, respectively, of the total cross section.