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 = 22,700 M(-1) cm(-1) for the 20 degrees 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.