Nonadiabatic quantum molecular dynamics with hopping. II. Role of nuclear quantum effects in atomic collisions

Abstract

The role of electron-nuclear correlations, i.e., quantum effects in the nuclear motion in atomic collisions with complex targets, is discussed using the recently developed nonadiabatic quantum molecular dynamics with hopping method [Fischer, Handt, and Schmidt, paper I of this series, Phys. Rev. A 90, 012525 (2014)]. It is shown that the excitation process is nearly unaffected by electron-nuclear correlations as long as integral quantities are considered (total kinetic energy loss), whereas the relaxation mechanism of the molecular target is greatly affected (total fragmentation probability). To describe highly differential quantities (kinetic energy loss as a function of the scattering angle), however, the consideration of nuclear quantum effects during the initial excitation process is indispensable, even in collisions where one would expect purely classical behavior of the nuclei due to their small de Broglie wavelength. The calculations reproduce and explain in detail old but still unexplained experimental data of differential energy-loss spectroscopy in $\mathrm{He}+\mathrm{He}$ and $\mathrm{He}+{\mathrm{H}}_{2}$ collisions.