The mechanism of electron-cation geminate recombination in liquid isooctane

Electron-cation geminate recombination in isooctane has been reinvestigated by femtosecond spectroscopy. The observed recombination kinetics are well-fit by a single exponential decay (τ = 400 ± 40 fs) and exhibit a significant hydrogen/deuterium kinetic isotope effect. The kinetics are not affected by varying the incident intensity or by exciting the recombining electrons with a high power 800 nm pulse. These observations strongly suggest that the recombination rate is not limited by diffusive motion of the ions to form a contact ion pair, but rather by the electron transfer reaction rate between the ions in a contact ion pair.