Interatomic Coulombic decay in lithium-doped large helium nanodroplets induced by photoelectron impact excitation

TL;DR

This study demonstrates that in large helium nanodroplets doped with lithium, indirect ionization via interatomic Coulombic decay induced by photoelectron scattering is highly efficient, revealing new insights into radiation effects in condensed matter.

Contribution

It uncovers a novel indirect ionization mechanism in helium nanodroplets involving ICD triggered by photoelectron scattering, which surpasses direct ionization methods.

Findings

Li ions are efficiently produced via ICD involving metastable He states.

Indirect ICD is more efficient than direct photoexcitation at 21.6 eV.

Photoelectron scattering induces ICD in large helium nanodroplets.

Abstract

Irradiation of condensed matter with ionizing radiation generally causes direct photoionization as well as secondary processes that often dominate the ionization dynamics. Here, large helium (He) nanodroplets with radius >40 nm doped with lithium (Li) atoms are irradiated with extreme ultraviolet (XUV) photons of energy >44.4 eV and indirect ionization of the Li dopants is observed in addition to direct photoionization of the He droplets. Specifically, Li ions are efficiently produced by an interatomic Coulombic decay (ICD) process involving metastable He atoms and He_2 excimers which are populated by elastic and inelastic scattering of photoelectrons in the nanodroplets as well as by electron-ion recombination. This type of indirect ICD, observed in large He nanodroplets in nearly the entire XUV range, turns out to be more efficient than Li dopant ionization by ICD following direct resonant photoexcitation at a photon energy of 21.6 eV and by charge-transfer ionization. Indirect ICD processes induced by scattering of photoelectrons likely play an important role in other condensed phase systems exposed to ionizing radiation as well, including biological matter.