On the lifetimes and physical nature of incompletely relaxed electrons in liquid water

Abstract

Despite intense study over the past two decades, the dynamics of electron solvation in water, particularly regarding the physical properties and lifetimes of non-equilibrium, incompletely relaxed electrons, remain very controversial. Both experimental and theoretical studies have reported a very diverse range, from ∼50 to ∼1000 fs, for the lifetime of the p-like excited state of the hydrated electron, and the nature of incompletely relaxed states remains unclear. Here, we reveal that these controversies are to a great extent due to a hidden effect, i.e., the universal existence of a coherence spike at delay time zero in pump–probe spectroscopic kinetics traces. After removing this spike effect, we show that the intrinsic lifetimes of the two incompletely relaxed states in bulk water are 180 ± 30 and 545 ± 30 fs, respectively. Moreover, our results using iododeoxyuridine as a molecular probe reveal that both states are electronically excited states of the hydrated electron and the second state of a 545 fs lifetime is the long-sought wet electron. These results resolve the long-standing controversies about electron hydration dynamics.