The solvated electron production by reaction between the H atom and the hydroxide anion was studied using Density Functional Theory based first-principles molecular dynamics. The simulation reveals a complex mechanism, controlled by proton transfers in the coordination sphere of the hydroxide and by the diffusion of the H atom in its solvent cavity. We formulate the hypothesis, based on a coupling between classical and first-principles molecular dynamics, that these two processes give rise to a lag time for the reaction that would explain the H atom extremely small reactivity compared to other radical species. Furthermore, the reaction observed gives an original insight in excess electron solvation.