Time-resolved Ultrafast Interatomic Coulombic Decay in Superexcited Sodium-doped Helium Nanodroplets

TL;DR

This study investigates ultrafast interatomic Coulombic decay (ICD) in superexcited sodium-doped helium nanodroplets using time-resolved XUV spectroscopy, revealing multiple decay channels, their time scales, and environmental influences on ICD efficiency.

Contribution

It provides the first detailed time-resolved analysis of ICD channels in superfluid helium nanodroplets doped with sodium, highlighting environmental effects and collective excitation influences.

Findings

ICD channels occur within ~1 ps, mainly influenced by droplet environment.

A periodic modulation suggests bubble oscillation around excited helium.

ICD efficiency depends on total excited states, indicating collective effects.

Abstract

The autoionization dynamics of superexcited superfluid He nanodroplets doped with Na atoms is studied by extreme-ultraviolet (XUV) time-resolved electron spectroscopy. Following excitation into the higher-lying droplet absorption band, the droplet relaxes into the lowest metastable atomic $1s2s$ $^{1,\,3}$S states from which Interatomic Coulombic Decay (ICD) takes places either between two excited He atoms or between an excited He atom and a Na atom attached to the droplet surface. Four main ICD channels are identified and their time constants are determined by varying the delay between the XUV pulse and a UV pulse that ionizes the initial excited state and thereby quenches ICD. The time constants for the different channels all fall in the range $\sim$1~ps indicating that the ICD dynamics are mainly determined by the droplet environment. A periodic modulation of the transient ICD signals is tentatively attributed to the oscillation of the bubble forming around the localized He excitation. The ICD efficiency depends on the total number of excited states in a droplet rather than the density of excited states pointing to a collective enhancement of ICD.