Ultrafast charge redistribution in small iodine containing molecules

TL;DR

This study investigates how ultrafast, element-specific charge redistribution occurs in small iodine-containing molecules after XUV photoionization, revealing molecule-specific electronic dynamics and differing fragmentation timescales.

Contribution

It demonstrates that charge redistribution immediately after ionization is highly molecule-specific and influences fragmentation behavior, combining experimental XUV-pump XUV-probe data with ab initio calculations.

Findings

Charge redistribution occurs rapidly and is molecule-specific.

Fragmentation timescales differ significantly between molecules.

Charge tends to localize on iodine atoms with lowest ionization potential.

Abstract

The competition between intra molecular charge redistribution and fragmentation has been studied in small molecules containing iodine by using intense ultrashort pulses in the extreme ultraviolet regime (XUV). We show that after an element specific inner-shell photoionization of diiodomethane (CH$_2$I$_2$) and iodomethane (CH$_3$I), the induced positive charge is redistributed with a significantly different efficiency. Therefore, we analyze ion time-of-flight data obtained from XUV-pump XUV-probe experiments at the Free Electron Laser in Hamburg (FLASH). Theoretical considerations on the basis of ab initio electronic structure calculations including correlations relate this effect to a strongly molecule specific, purely electronic charge redistribution process that takes place directly after photoionization causing a distribution of the induced positive charge predominantly on the atoms which exhibit the lowest atomic ionization potential, i.e, in the molecules considered, the iodine atom(s). As a result of the very different initial charge distributions, the fragmentation timescales of the two molecules experimentally observed are strikingly different.