FEMTOSECOND CHEMICAL-DYNAMICS IN SOLUTION - PHOTODISSOCIATION OF I-3(-)

We report a study of the UV photolysis of I-3(-) in alcohol solutions, using femtosecond time-resolved transient transmission experiments. W e interpret our results to indicate that photoexcitation leads to dire ct formation, within 300 fs, of diiodide ions which are vibrating cohe rently. The time scales for vibrational dephasing, vibrational relaxat ion, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps , respectively. UV transient transmission experiments were conducted i n order to characterize the time scales for recombination. Recombinati on takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the grou nd state of I-3(-). The prominence of this recombination route is foun d to be strongly dependent on the solvent. Finally, time domain quantu m simulation techniques are employed in order to gain insight into the nature of the nascent diiodide vibrational distribution, and to intro duce a semiquantitative model for the stage of bond fission for isolat ed ions.