Formation of anions and cations via a binary-encounter process in OH$^+$ + Ar collisions: the role of dissociative excitation and statistical aspects

TL;DR

This study investigates molecular fragmentation in OH$^+$ + Ar collisions at 7 keV, revealing similar angular distributions for H$^+$ and H$^-$ ions, and highlights the roles of binary encounters, dissociative excitation, and statistical charge distributions.

Contribution

It demonstrates the combined influence of binary-encounter dynamics and dissociative excitation in ion formation, with charge state populations explained by simple statistical laws.

Findings

H$^+$ and H$^-$ ions have similar angular dependences.

Kinetic energy distributions of H$^+$ and H$^-$ are similar.

Charge state populations follow statistical laws.

Abstract

Molecular fragmentation leading to the formation of negatively and positively charged hydrogen ions in 7-keV OH$^+$ + Ar collisions is investigated experimentally. The most striking finding is that negative and positive hydrogen ions are emitted with very similar angular dependences. Also, the kinetic energy distribution of the H$^+$ fragment shows strong similarities with that of the ejected H$^-$ ion. The kinematics of the emitted H core is found to be essentially driven by its scattering on the atomic target. However, in addition to this binary-encounter process, dissociative electronic excitation of the molecular projectile has to be invoked to explain the observed fragmentation patterns. Though the electron capture process is complex, it is shown that the relative population of the different final charge states of the outgoing fragments can be described by simple statistical laws.