Activation energy of the hydrated electron + water reaction and the ultra-violet absorption spectrum of the hydrated electron

Abstract

The ultra-violet absorption spectrum of the hydrated electron has been accurately determined down to 2200 Å where the molar extinction coefficient is 475 M^–1 cm^–1. A weak absorption with a lifetime of a few microseconds was noted below 3000 Å. This absorption was not due to either the OH, HO₂ or H₂O₂ species produced by the irradiation. The activation energy of the reaction e^– _aq+H₂O→H+OH^– has been determined, by rate measurements over the temperature range 5–81°C, as 6.7±0.7 kcal/mole. Combined with other thermodynamic data this value indicates that the reaction has a large negative entropy ΔS^≠ of activation of –22 cal/mole deg.