The electron photodetachment of the aqueous halides and hydroxide is studied after excitation in the lowest CTTS state.
The initially excited state is followed by an intermediate assigned to a donor-electron pair that displays a competition of
recombination and separation. The geminate dynamics measured in the various CTTS systems reveal a strong influence
of the parent radical. The electron survival probability decreases significantly from 0.77 to 0.29 going from F- to OH-.
Results for I- show that excitation of a higher-lying CTTS state opens a new relaxation channel, which directly leads to
fully hydrated electron, while the relaxation channel discussed above is not significantly affected. Using pump-repump-probe
spectroscopy the pair species is verified via a secondary excitation with separation of the pairs so that the yield of
released electrons is increased. Three pulse spectroscopy on aqueous hydroxide give evidence for an additional ultrafast
(~700 fs) geminate recombination channel in this system. Comparison of these data with similar experiments on neat
water after two-photon excitation with total energy of 9.2 eV demonstrates the important role of (OH-)* for the indirect
photoionization of water.
The electron photodetachment from 2.5~mM aqueous iodide solution is
studied in the temperature range 25 to 75°C. The dynamics
following excitation of the anion at 242~nm into the lowest CTTS state are studied in the spectral range of 400-1000~nm. A first intermediate is observed that builds up with a time constant of 220 to 180~fs in the investigated temperature interval and is assigned to an iodine:electron pair in a transient solvent configuration. Subsequent solvent reorganization leads to a quasi-equilibrated hydrated atom:electron pair (I:e-)hyd. The latter builds up with a time constant of 700 to 540~fs going from 25°C to 75°C. The following relaxation seems to be governed by partially diffusion-controlled recombination of the electron in the presence of an attraction potential well with depth of about 850~cm-1. The experimental result for the lifetime of the
hydrated I:e- pair is 21 to 16~ps going from 25°C to