The relaxation dynamics of superexcited superfluid He nanodroplets is thoroughly investigated by means of extreme-ultraviolet (XUV) femtosecond electron and ion spectroscopy complemented by time-dependent density functional theory (TDDFT). Three main paths leading to the emission of electrons and ions are identified: Droplet autoionization, pump-probe photoionization, and autoionization induced by re-excitation of droplets relaxing into levels below the droplet ionization threshold. The most abundant product of both droplet autoionization and photoionization is He2+, whereas the delayed appearance of He+ is indicative of the ejection of excited He atoms from the droplets. The state-resolved time-dependent photoelectron spectra reveal that intermediate excited states of the droplets are populated in the course of the relaxation, terminating in the lowest-lying metastable singlet and triplet He atomic states. The slightly faster relaxation of the triplet state compared to the singlet state is in agreement with the simulation showing faster formation of a bubble around a He atom in the triplet state.
@article{arxiv.2103.05948,
title = {Unravelling the Full Relaxation Dynamics of Superexcited Helium Nanodroplets},
author = {Jakob D. Asmussen and Rupert Michiels and Katrin Dulitz and Aaron Ngai and Ulrich Bangert and Manuel Barranco and Marcel Binz and Lukas Bruder and Miltcho Danailov and Michele Di Fraia and Jussi Eloranta and Raimund Feifel and Luca Giannessi and Marti Pi and Oksana Plekan and Kevin C. Prince and Richard J. Squibb and Daniel Uhl and Andreas Wituschek and Marco Zangrando and Carlo Callegari and Frank Stienkemeier and Marcel Mudrich},
journal= {arXiv preprint arXiv:2103.05948},
year = {2021}
}