Tabletop Core-to-Valence Transient Absorption Spectroscopy of Ultrafast Gas-Phase Chemical Dynamics

Ultrafast core-to-valence transient absorption spectroscopy has emerged as a powerful technique for monitoring nonequilibrium chemical dynamics with element and site specificity. Owing to advancements in the robust, tabletop generation of ultrafast extreme ultraviolet (XUV) and soft X-ray (SXR) pulses, this technique has been applied to great effect in investigating electronic excited-state dynamics in various gas-phase molecules. This review begins with an overview of the experimental advances that have enabled laboratory-scale XUV and SXR production with particular emphasis on high-harmonic generation, central to modern implementations of tabletop core-to-valence transient absorption spectroscopy. We then highlight a collection of landmark studies that demonstrate the unprecedented insights this technique yields into the site-specific excited-state dynamics governing photoinduced processes such as bond dissociation, conformational change, and electronic relaxation in gas-phase molecules. We conclude with an outlook on future frontiers, including control of excited-state dynamics, other nonlinear X-ray spectroscopies, and next-generation light sources.