All-XUV Pump-Probe Transient Absorption Spectroscopy of the Structural Molecular Dynamics of Di-iodomethane

In this work, we use an extreme-ultraviolet (XUV) free-electron laser (FEL) to resonantly excite the I:4d(5/2)(-sigma*) transition of a gas-phase di-iodomethane (CH2I2) target. This site-specific excitation generates a 4d core hole located at an iodine site, which leaves the molecule in a well-defined excited state. We subsequently measure the time-dependent absorption change of the molecule with the FEL probe spectrum centered on the same I: 4d resonance. Using ab initio calculations of absorption spectra of a transient isomerization pathway observed in earlier studies, our time-resolved measurements allow us to assign the timescales of the previously reported direct and indirect dissociation pathways. The presented method is thus sensitive to excited-state molecular geometries in a time-resolved manner, following a core-resonant site-specific trigger.

Automated summary

In this study, an extreme-ultraviolet free-electron laser is used to excite a gas-phase di-iodomethane target, allowing for the investigation of molecular dissociation pathways and geometries in a time-resolved manner. The method presented in this work provides a sensitive approach to study excited-state molecular structures and reactions triggered by core-resonance at specific sites.