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

摘要

In this work, we use an extreme-ultraviolet (XUV) free-electron laser (FEL) to resonantly excite the I : 4 d 5 / 2 – σ * transition of a gas-phase di-iodomethane ( CH 2 I 2 ) target. This site-specific excitation generates a 4 d 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 : 4 d 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.