Predissociation dynamics of lithium iodide

TL;DR

This study investigates the ultrafast predissociation dynamics of lithium iodide in the gas phase and helium nanodroplets using femtosecond spectroscopy, revealing the role of potential curve crossings and droplet-induced relaxation.

Contribution

It combines experimental femtosecond pump-probe spectroscopy with high-level ab initio calculations to elucidate LiI predissociation mechanisms in different environments.

Findings

Predissociation occurs mainly at the X-A potential curve crossing.

Vibrational wave packets decay exponentially due to predissociation.

Helium nanodroplets induce rapid vibrational relaxation.

Abstract

The predissociation dynamics of lithium iodide (LiI) in the first excited A-state is investigated for molecules in the gas phase and embedded in helium nanodroplets, using femtosecond pump-probe photoionization spectroscopy. In the gas phase, the transient Li+ and LiI+ ion signals feature damped oscillations due to the excitation and decay of a vibrational wave packet. Based on high-level ab initio calculations of the electronic structure of LiI and simulations of the wave packet dynamics, the exponential signal decay is found to result from predissociation predominantly at the lowest avoided X-A potential curve crossing, for which we infer a coupling constant V=650(20) reciprocal cm. The lack of a pump-probe delay dependence for the case of LiI embedded in helium nanodroplets indicates fast droplet-induced relaxation of the vibrational excitation.