# Theoretical evidence for the sensitivity of charge-rearrangement-enhanced x-ray ionization to molecular size

## TL;DR

This theoretical study shows that charge-rearrangement-enhanced x-ray ionization (CREXIM) increases with molecular size, leading to higher ionization levels in larger molecules due to enhanced intramolecular electron transfer during XFEL interactions.

## Contribution

The paper provides the first theoretical evidence that CREXIM effects grow with molecular size, highlighting the importance of electron transfer dynamics in large molecules under intense x-ray pulses.

## Key findings

- CREXIM effect increases with molecular size.
- Larger molecules like iodobenzene show higher ionization than smaller ones.
- Charge redistribution occurs from iodine to the benzene ring.

## Abstract

It was recently discovered that molecular ionization at high x-ray intensity is enhanced, in comparison with that of isolated atoms, through a phenomenon called CREXIM (charge-rearrangement-enhanced x-ray ionization of molecules). X-ray absorption selectively ionizes heavy atoms within molecules, triggering electron transfer from neighboring atoms to the heavy atom sites and enabling further ionization there. The present theoretical study demonstrates that the CREXIM effect increases with the size of the molecule, as a consequence of increased intramolecular electron transfer from the larger molecular constituents attached to the heavy atoms. We compare x-ray multiphoton ionization dynamics of xenon, iodomethane, and iodobenzene after interacting with an intense x-ray pulse. Although their photoionization cross sections are similar, iodomethane and iodobenzene molecules are more ionized than xenon atoms. Moreover, we predict that the average total charge of iodobenzene is much larger than that of iodomethane, because of the large number of electrons in the benzene ring. The positive charges transferred from the iodine site to the benzene ring are redistributed such that the higher carbon charges are formed at the far end from the iodine site. Our first-principles calculations provide fundamental insights into the interaction of molecules with x-ray free-electron laser (XFEL) pulses. These insights need to be taken into account for interpreting and designing future XFEL experiments.