Probing the UV-Induced Photodissociation of CH$_\text{3}$I and C$_\text{6}$H$_\text{3}$F$_\text{2}$I with Femtosecond Time-Resolved Coulomb Explosion Imaging at FLASH

TL;DR

This study demonstrates the use of femtosecond XUV pulses from FLASH to image molecular dynamics during UV-induced photodissociation of iodomethane and difluoroiodobenzene, revealing charge transfer and ultrafast charge rearrangement.

Contribution

It introduces a novel application of time-resolved Coulomb explosion imaging with XUV pulses to study molecular dissociation and charge dynamics in complex molecules.

Findings

XUV pulses induce local iodine ionization in dissociating molecules.

Evidence of electron transfer from molecular fragments to iodine ions.

Detection of ultrafast charge rearrangement in phenyl radicals.

Abstract

We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from the FLASH free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267\,nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon--iodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local inner-shell ionization of atomic iodine in dissociating iodomethane, in contrast to non-selective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that time-resolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules.