Time-resolved scavenging and recombination dynamics from I:e[sup -] caged pairs.

The competition between geminate recombination of electrons with their parent radicals and electron scavenging with H[sup +] is directly time resolved with ∼100 fs resolution at several acid concentrations. Electrons were produced from iodide photodetachment or two-photon ionization of H[sub 2]O. With regards to those produced from iodide photodetachment, the separation between primary and secondary I:e[sup -] recombination is established using a full numerical solution to the diffusion equation. Electron ejection is found to be short range and a potential well of ∼3k[sub b]T depth stabilizing the solvent caged pair is required to yield a satisfactory fit to experiment. From time-resolved scavenging data up to 5 M HCl, it is shown that the electron can be scavenged both inside and outside the caged pair by H[sup +] with nearly equal efficiency. The steady-state scavenging yield as a function of scavenger concentration is then predicted based on the determined time-dependent recombination function. Reassessment of several benchmark scavenging experiments from the 1960's leads to the conclusion that the primary yield of electrons after excitation of iodide is near unity. [ABSTRACT FROM AUTHOR]