Vibrational relaxation of hot ground state cations of naphthalene

TL;DR

This study uses time-resolved XUV-IR spectroscopy to investigate vibrational energy redistribution in naphthalene cations, revealing a consistent 92 fs relaxation time linked to vibrational mode population changes.

Contribution

It provides new insights into vibrational relaxation dynamics of naphthalene cations using combined experimental and statistical modeling approaches.

Findings

Vibrational relaxation lifetime of 92 fs observed.

Fragmentation probability increases independently of excitation wavelength.

Vibrational modes like ring twist and wave bending influence fragmentation channels.

Abstract

Time-resolved XUV-IR photoion mass spectroscopy of naphthalene conducted with broadband, as well as with wavelength-selected narrowband XUV pulses reveals a rising probability of fragmentation characterized by a lifetime of $92\pm4$~fs. This lifetime is independent of the XUV excitation wavelength and is the same for all low appearance energy fragments recorded in the experiment. Analysis of the experimental data in conjunction with a statistical multi-state vibronic model suggests that the experimental signals track vibrational energy redistribution on the potential energy surface of the ground state cation. In particular, populations of the out-of-plane ring twist and the out-of-plane wave bending modes could be responsible for opening new IR absorption channels leading to enhanced fragmentation.