Photodissociation of aligned CH3I and C6H3F2I molecules probed with time-resolved Coulomb explosion imaging by site-selective extreme ultraviolet ionization.

Kasra Amini,Nora Schirmel,Michael Burt,Jason W L Lee,Daniel Rolles,Cédric Bomme,Joss Wiese,Artem Rudenko,Erland Müller,Hauke Höppner,Anatoli Ulmer,Jan Thøgersen,Evgeny Savelyev,Benjamin Erk,Rebecca Boll,Arnaud Rouzée,Felix Brauße,Jochen Küpper,Per Johnsson,Simone Techert,Claire Vallance,Sebastian Trippel,Thomas Kierspel,Alexandra Lauer,Henrik Stapelfeldt,Lars Rune Christensen ,H Redlin ,S Toleikis ,M Müller ,Faruk Krečinić ,Terry Mullins ,M Brouard ,S Düsterer ,N Berrah ,R Treusch

doi:10.1063/1.4998648

Abstract

We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a 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.

Highlights

If several electrons are rapidly removed from a molecule, it fragments into cations by a process termed Coulomb explosion.1 Provided that the break-up occurs faster than vibrational motion, the momenta of the fragments can be used to determine the structure of gas-phase molecules
We explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and
We focus on the molecular dynamics due to the UVdissociation and the subsequent XUV-induced Coulomb explosion and on the comparison between DFIB and CH3I molecules

Summary

INTRODUCTION

If several electrons are rapidly removed from a molecule, it fragments into cations by a process termed Coulomb explosion. Provided that the break-up occurs faster than vibrational motion, the momenta of the fragments can be used to determine the structure of gas-phase molecules. We focus on the role of site-selective ionization in time-resolved Coulomb explosion imaging experiments To this end, we investigate the ultraviolet (UV)-induced photoexcitation and subsequent XUV ionization and fragmentation of isolated iodomethane (CH3I) and 2,6difluoroiodobenzene (C6H3F2I, DFIB) molecules, see Fig. 1. At a certain time delay after the UV excitation, the dissociating molecule is ionized by the free-electron laser probe pulse, leading to a highly excited molecular ion that fragments through Coulomb explosion. This is illustrated, showing one-dimensional cuts through the potential energy hypersurfaces of the multiply charged molecular ion which are formed following (multiple)

EXPERIMENT

RESULTS

CONCLUSION AND OUTLOOK