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

摘要

The competition between geminate recombination of electrons with their parent radicals and electrons cavenging with H~+ is directly time resolved with approx100 fs resolution at several acid concentrations.Electrons were produced from iodide photodetachment or two-photon ionization of H_2O.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 approx3kbT 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.