Femtosecond Chemical Dynamics in Solution: Photodissociation of I₃‐

We report a study of the UV photolysis of I₃⁻ in alcohol solutions, using femtosecond time‐resolved transient transmission experiments. We interpret our results to indicate that photoexcitation leads to direct formation, within 300 fs, of diiodide ions which are vibrating coherently. The time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. UV transient transmission experiments were conducted in order to characterize the time scales for recombination. Recombination takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the ground state of I₃⁻. The prominence of this recombination route is found to be strongly dependent on the solvent. Finally, time domain quantum simulation techniques are employed in order to gain insight into the nature of the nascent diiodide vibrational distribution, and to introduce a semiquantitative model for the stage of bond fission for isolated ions.