Hydrated Electron Extinction Coefficient Revisited

The extinction coefficient of the hydrated electron (e−)aq generated by pulse radiolysis is evaluated relative to the methyl viologen radical cation •MV+, whose extinction coefficient at 605 nm has been carefully measured in the past. We find that the room temperature (e−)aq extinction coefficients reported in the literature are underestimated by 10−20%. We obtain ϵ = 22 700 M−1 cm−1 for the 20 °C hydrated electron at 720 nm, assuming the •MV+ extinction is 13 700 M−1 cm−1 at 605 nm. This has implications both for second-order reaction rate measurements of (e−)aq and for the estimate of its integrated oscillator strength.