Probing ultrafast dynamics in aqueous pyrazine solution using liquid microjet based time-resolved photoelectron spectroscopy

An aqueous environment plays an important role in chemical and energy transfer process in biological, environmental and energy science. Pyrazine has been studied extensively in the gas phase showing rich photo physiochemical properties. Because of the high solubility and high photo absorption cross-section, pyrazine is an ideal candidate to probe changes in electronic structure and associated ultrafast chemical dynamics in aqueous solution. The experiment was performed using low intensity 266 nm pump pulses to directly access the photoexcited S₂ state under conditions that suppress any multi-photon ionization-induced space charge effects. The ground and excited states were simultaneously photoexcited using 32 nm ultrashort extreme ultraviolet (EUV) pulses. Due to electrostatic interactions and hydrogen bonding in the aqueous solution, the ultrafast dynamics are modified compared to gas phase pyrazine. Our preliminary results indicate that on initial ultrafast internal conversion occurs in 81 ± 10 fs. Subsequent electron transitions proceed on 450 ± 90 fs and 80 ± 20 ps timescales. In this talk, the electronic energetics and associated ultrafast relaxation mechanism of aqueous pyrazine will be presented and compared to corresponding gas-phase results.