Articles you may be interested inOne-photon photodetachment of I − in glycerol: Spectra and yield of solvated electrons in the temperature range 329 T 536 K Mechanisms of the ultrafast production and recombination of solvated electrons in weakly polar fluids: Comparison of multiphoton ionization and detachment via the charge-transfer-to-solvent transition of Na − in THF The spectra and the relative yield of solvated electrons produced by resonant photodetachment of iodide anion in ethylene glycol in the temperature range 296T453 K Two-photon dissociation and ionization of liquid water studied by femtosecond transient absorption spectroscopyThe ultrafast dynamics following one-photon UV photodetachment of I Ϫ ions in aqueous solution are compared with those following two-photon ionization of the solvent. Ultrafast pump-probe experiments employing 50 fs ultraviolet pulses reveal similar and very rapid time scales for electron ejection. However, the electron ejection process from water pumped into the conduction band and from iodide ions detached at threshold are readily distinguishable. The observed picosecond timescale geminate recombination and electron escape dynamics are reconstructed using two different models, a diffusion-limited return of the electron from ϳ15 Å to its parent and a competing kinetics model governed by the reverse electron transfer rate. We conclude that the ''ejected'' electron in the halide detachment is merely separated from the halogen atom within the same solvent shell. The assignment of detachment into a contact pair is based on the recombination profile rather than by the postulate of any new spectral absorption due to an electron in a contact pair. The contact pair is surprisingly long-lived and the nonadiabatic recombination is rather slow considering the proximity of the partners. Experiments in mixed solvents confirm our assignment of the two distinct ejection mechanisms. The detachment mechanism is therefore fundamentally different in the resonant ͑one photon͒ charge-transfer-to-solvent ͑CTTS͒ process from the multiphoton detachment of aqueous iodide ions, which bears more similarity to the direct solvent ionization.

The early time dynamics of electron photoejection and relaxation after one-photon UV photodetachment of iodide ions in aqueous solution is compared with that resulting from two-photon ionization of neat water. The effect of solvent composition on the ejection and relaxation is probed via experiments on iodide photodetachment in a water/ethylene glycol mixture. Representation of our pump−multiple wavelength probe experimental data sets as two-dimensional contour plots provides a convenient fingerprint of the electron dynamics. Global fitting of the data to a solvation model for spectral evolution indicates varying time scales for solvation for each of the ejection systems. In all cases, the spectral evolution is complete in the first 10 ps, however electrons ejected via the anion charge-transfer-to-solvent pathway relaxes by a factor of 2 slower. For iodide detachment in the water/glycol mixture, evidence is found for a precursor excess electron state in the infrared that decays on the order of 250 fs. No evidence for an electron precursor state is found for the ionization of water within the 400−1000 nm window studied, and the ground state is apparent within 200 fs. From these results, and from picosecond scale recombination dynamics presented elsewhere (Kloepfer et al. J. Chem. Phys. 2000, 113, 6288−6307), we conclude that the electron production mechanism is distinct for the anion detachment and solvent ionization pathways.

The competition between geminate recombination of electrons with their parent radicals and electron scavenging with H+ is directly time resolved with ∼100 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 ∼3kbT 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.

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