UV photolysis of in solution – Multiple product channels detected by transient hyperspectral probing

Recombination of triiodide is followed in several polar liquids using femtosecond hyperspectral probing. Results reveal narrowing and blue shifting in product absorbance for tens of picoseconds coinciding with a delayed stage of geminate recombination. Global kinetic analysis suggests both can be assigned to a distinct fragment population other than free solvated diiodide, most likely caged [ · I 2 - ; · I ] contact pairs. Interaction between the fragments is proposed to alter oscillator strengths and transition energies of the diiodide absorption bands, with the spectral evolution reflecting recombination of contact pairs to regenerate I 3 - . Charge transfer between the caged fragments is proposed to be the step determining the rates of recombination explaining its delayed nature.