Rapid solvent-induced recombination and slow energy relaxation in a simple chemical reaction: Picosecond studies of iodine photodissociation inCCl4

The time scale for solvent ‘‘caging’’ in the classic ${\mathrm{I}}_2$ photodissociation reaction appears to be ≤15 ps, on the basis of examination of new picosecond absorption spectra. The previously observed slow recovery (>100 ps) of molecular absorption is shown to be due to both ground-state vibrational relaxation and excited-state trapping in the recombined molecule. In addition, newly observed absorptions in the 350–400-nm region provide direct information on solvent-induced predissociation and excited-state vibrational relaxation.