Concurrent processes in the time-resolved solvation and Coulomb ejection of sodium ions in helium nanodroplets

TL;DR

This paper uses atomistic simulations to investigate the rapid processes of sodium ion solvation, shell formation, and Coulomb ejection in helium nanodroplets, revealing their dependence on ionization timing and droplet size.

Contribution

It provides a detailed computational analysis of the ultrafast ionization and solvation dynamics in helium nanodroplets, highlighting the interplay of these processes.

Findings

Ionization, shell formation, and Coulomb ejection occur within tens of picoseconds.

The processes depend on the time delay between ionizations.

Formation of solvated Na$^+$Xe complexes is unlikely within this timescale.

Abstract

Recent pump-probe experiments [Albrechtsen {\em et al.}, Nature {\bf 623}, 319 (2023)] have explored the gradual solvation of sodium cations in contact with helium nanodroplets, using a fully solvated xenon atom as a probe exerting a repulsive interaction after its own ionization. In this Communication we computationally examine by means of atomistic ring-polymer molecular dynamics the mechanisms of successive ionizations, shell formation, and Coulomb ejection that all take place within tens of picoseconds, and show that their interplay subtly depends on the time delay between the two ionizations but also on the droplet size. The possibility of forming solvated Na$^+$Xe non-covalent complexes under a few tens of picoseconds in such experiments is ruled out based on fragment distributions.