Lack of ionic strength effect in the recombination of hydrated electrons: (e−)aq + (e−)aq → 2(OH−) + H2 Original Research Article

We report measurements of the rate constant for bimolecular reaction between hydrated electrons in the presence of added inert salt. At 23°C, the rate constant is 6.0 × 109 M−1 s−1, virtually independent of added LiClO4 up to 0.06 M concentration, where the Bronsted-Bjerrum equation would predict a 50% rate enhancement. However, the diffusion rate of ions is reduced by the additional friction from the ionic atmosphere. We demonstrate that for this peculiar diffusion-limited reaction the two effects counterbalance, producing almost no change in the reaction rate. Based on the large reaction distance and activation energy, it appears that a solvent-separated singlet pair of electrons is stable relative to kT.