In situ generation and reaction of a sub-picosecond electron pulse: ultrafast broadband spectroscopy

A sub-picosecond resolved broadband transient absorption spectrometer for in situ generation and study of ultrafast reaction of short pulse electrons in water has been reported. A femtosecond near infrared (NIR) laser driven multiphoton ionization of water was used for the in situ generation of an ultra-short electron pulse in aqueous media. The dynamics of such electrons have been investigated using a broadband pump-probe spectrometer with a temporal resolution of sub-picosecond. The formation of the pre-hydrated electron having absorption in the NIR region and its subsequent solvation process leading to the formation of the hydrated electron has been monitored in real time using pump-probe spectroscopy. As a proof of concept, a reaction of pre-hydrated electrons and hydrated electrons with a highly oxidizing agent, methyl viologen, has been carried out. The competition of the reaction with methyl viologen and solvent relaxation of the pre-hydrated electron has been demonstrated by broadband ultrafast spectroscopy. Our results show that the reactivity of pre-hydrated electrons with methyl viologen is almost two orders of magnitude higher as compared to the hydrated electrons. Unlike complicated laser driven accelerators, the present table-top setup for the generation of an in situ ultrashort electron pulse and its reaction with different classes of molecules, especially biomolecules, will help us understand the early events of radiation-induced processes under reductive stress.