Time-resolved scavenging and recombination dynamics from l:e- caged pairs

The competition between geminate recombination of electrons with their parent radicals and electron scavenging with H+ is directly time resolved with similar to100 fs resolution at several acid concentrations. Electrons were produced from iodide photodetachment or two-photon ionization of H2O. With regards to those produced from iodide photodetachment, the separation between primary and secondary I:e(-) 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 similar to3k(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+ 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. (C) 2002 American Institute of Physics.