Goal: Identify the instantaneous, radiation-induced changes to electronic structure that determine the reactive species in concentrated electrolytes.

Experimental Lead: Linda Young, Theory Lead: Xiaosong Li

A microscopic understanding of the first stages of radiolysis—characterized by energy deposition and molecular ionization/excitation on the attosecond timescale, rapidly followed by secondary electron emissions with the formation of new reactive chemical species on the femtosecond timescale—remains elusive experimentally and theoretically. In STaR 1, we are employing (1) femtosecond and/or attosecond ionization pump sources and (2) femtosecond and/or attosecond X-ray or IR probes to track transient species on timescales ranging from attoseconds to picoseconds. Theoretically, we are employing first-principles quantum chemistry methods to model evolving excited-state electronic structures and their spectroscopic signatures in these complex systems. These methods are  based on the latest developments in electronic structure theory, in which nuclear and electronic wave functions are evolved simultaneously in real time. We are dissecting the radiolysis process at a molecular level by systematically varying the ultrafast ionization sources to target selectively outer- and inner-shell ionization. We are investigating the dynamics following outer-valence ionization—creating single electron–hole pairs in complex solutions. We are also examining the dynamics following full-valence-band (or core) ionization, closely resembling the lower-energy b or g radiolysis in the waste tanks.

Our recently developed methods to ionize and probe the appearance of new species and the evolution of electronic structure in the solution phase on ultrafast timescales are foundational to STaR 1. We are extending our proof-of-concept ultrafast radiolysis studies beyond water and into the heterogeneous local environments of concentrated electrolytes.