Quantitative Classical Relaxation Dynamics of Penning-Ionized He/Ne--H$_2^+$/HD$^+$ Complexes

Abstract

Penning ionization allows {\it in situ} generation of ionic complexes to launch vibrational relaxation and dissociation dynamics for rare gas--H$_2^+$/HD$^+$ complexes. The ensuing translational kinetic energy release (TKER) spectra characterizing the diatomic cation are a particularly sensitive way to probe the long range part of the intermolecular interactions. TKER distributions from quasi-classical trajectory (QCT) simulations for the Ne--H$_2^+$ and Ne--HD$^+$ complexes quantitatively match measured positions and relative intensities of most experimentally observed features and are also on par with time-dependent quantum simulations. Specifically, the QCT-simulations allow to separate signatures arising from H$_2^+$/HD$^+$ relaxation into different final vibrational states, such as for $(v=2) \rightarrow (v' = 0/1 )$. Trajectory-resolved QCT analysis also provides mechanistic interpretations of the spatial and time-dependent dynamics underlying the TKER distributions. Rare gas--H$_2^+$/HD$^+$ complex lifetimes directly correlate with the final rotational quantum number $j'$ of the diatomic. Low-$j'$ products are associated primarily with an initial axial approach of the rare gas atom, whereas formation of higher-$j'$ states predominantly results from an initial T-shaped approach geometry.