GEMINATE RECOMBINATION AND VIBRATIONAL-RELAXATION DYNAMICS OF AQUEOUSCHLORINE DIOXIDE - A TIME-RESOLVED RESONANCE RAMAN-STUDY

The photochemical dynamics of aqueous chlorine dioxide (OClO) are inve stigated using time-resolved resonance Raman spectroscopy. Stokes and anti-Stokes spectra are measured as a function of time following photo excitation of OClO using degenerate pump and probe wavelengths at 390 nm. The temporal evolution of OClO Stokes intensity is found to be con sistent with the reformation of ground-state OClO by subpicosecond gem inate recombination of the primary ClO and O photofragments. Anti-Stok es intensity is observed for transitions corresponding to the symmetri c stretch of OClO demonstrating that upon geminate recombination, exce ss vibrational energy is deposited along this coordinate. Dissipation of this energy to the surrounding solvent occurs with a time constant of similar to 9 ps. Finally, a delay in the appearance of OClO anti-St okes intensity relative to geminate recombination is observed demonstr ating that the excess vibrational energy available to OClO is initiall y deposited along the resonance Raman inactive asymmetric stretch coor dinate with the exchange of energy between this coordinate and the sym metric stretch occurring with a time-constant of similar to 5 ps. (C) 1998 American Institute of Physics.