Charge-exchange dominates long-range interatomic Coulombic decay of excited metal-doped He nanodroplets

TL;DR

This study reveals that in excited metal-doped helium nanodroplets, charge exchange is the dominant mechanism for long-range interatomic Coulombic decay, with ultrafast droplet relaxation observed through electron spectra.

Contribution

It demonstrates that charge exchange ICD dominates long-range autoionization in metal-doped helium nanodroplets, supported by experimental coincidence measurements and ab initio calculations.

Findings

Charge exchange ICD dominates long-range autoionization.

Ultrafast internal relaxation into specific excited states.

Electron spectra show rapid droplet relaxation processes.

Abstract

Atoms and molecules attached to rare gas clusters are ionized by an interatomic autoionization process traditionally termed 'Penning ionization' when the host cluster is resonantly excited. Here we analyze this process in the light of the interatomic Coulombic decay (ICD) mechanism, which usually contains a contribution from charge exchange at short interatomic distance, and one from virtual photon transfer at large interatomic distance. For helium (He) nanodroplets doped with alkali metal atoms (Li, Rb), we show that long-range and short-range contributions to the interatomic autoionization can be clearly distinguished by detecting electrons and ions in coincidence. Surprisingly, ab initio calculations show that even for alkali metal atoms floating in dimples at large distance from the nanodroplet surface, autoionization is largely dominated by charge exchange ICD. Furthermore, the measured electron spectra manifest ultrafast internal relaxation of the droplet into mainly the 1s2s 1^S state and partially into the metastable 1s2s 3^S state.