Interatomic Coulombic decay initiated by electron removal and excitation processes in helium ion and argon dimer collisions

TL;DR

This study investigates the mechanisms of interatomic Coulombic decay (ICD) in helium ion and argon dimer collisions, revealing dominant excitation channels and the influence of projectile energy and charge state on ICD processes.

Contribution

It introduces a comprehensive theoretical framework combining coupled-channel methods and statistical analysis to elucidate ICD pathways in ion-dimer collisions, highlighting the role of specific excited states.

Findings

$3d$ excited state is a dominant ICD channel

ICD pathways are influenced by projectile charge and energy

Dynamical models show decreasing differences at higher impact energies

Abstract

The electron removal and excitation channels in argon dimer target and helium ion projectile collision systems that facilitate interatomic Coulombic decay (ICD) are investigated. We implement an independent-atom and independent-electron model of the collision system with the dimer target fixed at its equilibrium bond length and the He$^{2+}$ and He$^+$ ion projectiles travelling parallel to the dimer axis at impact energies ranging from 10 keV/amu to 150 keV/amu. The coupled-channel two-center basis generator method for orbital propagation is used within both a frozen atomic target approximation and a dynamic response framework. Given that ICD is facilitated through electron excitation pathways in argon dimers, a statistical technique called determinantal analysis is employed to investigate these channels. The analysis is further subdivided into models that exclude and include projectile charge changes during the collision. Electron configurations of the form Ar$^{+}$($3p^{-2}nl$) offer a pathway to ICD and are investigated, along with other one- and two-electron removal channels that lead to Ar$^{+}$-Ar$^{+}$ fragmentation. We find that the $3d$ excited state is an overall dominant channel for ICD with other excited states ranging from $4s$-$4f$ also being significant contributors. Our study notes differences between static and dynamical potential models across the projectile impact energy range, though of decreasing significance as the impact energy approaches 150 keV/amu. We also find that a He$^{+}$ projectile offers a strong pathway for ICD as the projectile impact energy decreases.