# Time-resolved inner-shell photoelectron spectroscopy: from a bound molecule to an isolated atom

## TL;DR

This paper demonstrates that time-resolved inner-shell photoelectron spectroscopy can effectively observe ultrafast chemical reactions and electronic responses in molecules, providing high sensitivity to structural and electronic changes.

## Contribution

It introduces the application of time-resolved inner-shell photoelectron spectroscopy to monitor ultrafast molecular dynamics with element-specific sensitivity.

## Key findings

- Ultrafast dynamics observed earlier in photoelectron spectra than in fragment signals
- Spectroscopic evidence of electronic and structural changes during dissociation
- Validation of the technique through theoretical calculations

## Abstract

Due to its element- and site-specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH$_3$I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.