Femtosecond photoexcitation dynamics inside a quantum solvent

TL;DR

This study investigates the ultrafast solvent response to photoexcitation of indium atoms in helium nanodroplets, revealing shell expansion and oscillations using femtosecond spectroscopy and theoretical simulations.

Contribution

It provides a mechanistic understanding of the femtosecond solvent dynamics in a quantum solvent, combining experimental and computational approaches.

Findings

Solvation shell expands within 600 fs after excitation.

Shell oscillates with a period of about 30 ps.

Electronic energy leads to collective solvent motion.

Abstract

The observation of chemical reactions on the time scale of the motion of electrons and nuclei has been made possible by lasers with ever shortened pulse lengths. Superfluid helium represents a special solvent that permits the synthesis of novel classes of molecules that have eluded dynamical studies so far. However, photoexcitation inside this quantum solvent triggers a pronounced response of the solvation shell, which is not well understood. Here we present a mechanistic description of the solvent response to photoexcitation of indium (In) dopant atoms inside helium nanodroplets (He$_\mathrm{N}$), obtained from femtosecond pump-probe spectroscopy and time-dependent density functional theory simulations. For the In-He$_\mathrm{N}$ system, part of the excited state electronic energy leads to expansion of the solvation shell within 600 fs, initiating a collective shell oscillation with a period of about 30 ps. These coupled electronic and nuclear dynamics will be superimposed on intrinsic photoinduced processes of molecular systems inside helium droplets.