Static and dynamic scavenging of ammoniated electrons by nitromethane

We studied the time-resolved scavenging efficiency of nitromethane for transient electron species in liquid ammonia, at a temperature of 298 K. UV excitation of iodide ions produced fully solvated electrons, as well as transient (I, e(-)) and (counterion, e(-)) pairs, the overall concentration of which was monitored by NIR absorption with subpicosecond time resolution. After the UV pulse, the solution absorbance decays almost completely in a few hundreds of picoseconds due to geminate electron-iodine atom recombination and a competitive annihilation channel involving the scavenger. Recombination of transient (I, e(-)) pairs follows the well-known kinetic model, while the electron-nitromethane reaction proceeds by two distinct mechanisms: static scavenging (interpreted in terms of the encounter complex model), with a characteristic time shorter than the temporal resolution of the apparatus, or via a diffusion-limited bimolecular reaction, with a rate constant of 1.1 x 10(11) M-1 s(-1).