Photo-induced dynamics of isolated chromophore anions

Dr James Bull

School of Chemistry, University of Melbourne, Australia

This talk will detail two action spectroscopy techniques deployed to probe the photophysics and excited state dynamics of “large” gas-phase electrophore and chromophore anions: (i) frequency-, angle- and time-resolved photoelectron imaging (FAT-PI) and (ii) tandem ion mobility mass spectrometry (IMMS) coupled with laser spectroscopy. I will first introduce velocity-map imaging and FAT-PI through characterisation of the sub-picosecond internal conversion dynamics in menadione (vitamin K₃) radical anions. The FAT-PI technique has been applied to a wide variety of other chromophore anions, including for the formation and autodetachment dynamics of a dipole-bound state (a non-valence state bound through dipolar forces) in cluster anions and for the first characterisation of an elusive correlation-bound state (a non-valence state bound through electron correlation forces). The second part of this talk will introduce IMMS through the photo-induced and thermal E-Z isomerisation of Congo Red dianions. Our IMMS technique enables study of the photo-induced responses of ‘shape-selected’ ions by exploiting differences in their collision cross-section with a buffer gas (e.g. N₂ or CO₂). The majority of other action spectroscopies are not selective for one isomer or deprotomer and are blind to any photo-induced intramolecular processes that may ensue in the gas phase. The final part of the talk will detail current efforts to combine data sets recorded using both techniques, allowing for rigorous characterisation of multiple competitive pathways, including autodetachment, isomerisation, internal conversion, and formation of non-valence states.