Hydrated electron dynamics: From clusters to bulk

The electronic relaxation dynamics of size-selected (H2O)(n)(-)/(D2O)(n)(-)[25less than or equal tonless than or equal to50] clusters have been studied with time-resolved photoelectron imaging. The excess electron (e(c)(-)) was excited through the e(c)(-)(p)<--e(c)(-)(s) transition with an ultrafast laser pulse, with subsequent evolution of the excited state monitored with photodetachment and photoelectron imaging. All clusters exhibited p-state population decay with concomitant s-state repopulation (internal conversion) on time scales ranging from 180 to 130 femtoseconds for (H2O)n- and 400 to 225 femtoseconds for (D2O)(n)(-); the lifetimes decrease with increasing cluster sizes. Our results support the "nonadiabatic relaxation" mechanism for the bulk hydrated electron (e(aq)(-)), which invokes a 50-femtosecond e(aq)(-) (p)-->e(aq)(-) (s(dagger)) internal conversion lifetime.