Intermolecular hydrogen bonding in chlorine dioxide photochemistry: A time-resolved resonance Raman study

Abstract

The geminate recombination and vibrational relaxation dynamics of chlorine dioxide (OClO) dissolved in ethanol and 2,2,2-trifluoroethanol (TFE) are investigated using time-resolved resonance Raman spectroscopy. Stokes spectra are measured as a function of time following photoexcitation using 398-nm degenerate pump and probe wavelengths. In ethanol, subpicosecond reformation of ground-state OClO through recombination of the primary photofragments occurs with a quantum yield of 0.5 ± 0.1. Following recombination, intermolecular vibrational relaxation occurs with a time constant of 31 ± 10 ps. For OClO dissolved in TFE, recombination occurs with a time constant of 1.8 ± 0.8 ps and quantum yield of only 0.3 ± 0.1. In addition, intermolecular vibrational relaxation occurs with a time constant of 79 ± 27 ps. The decreased geminate-recombination quantum yield and vibrational-relaxation rate for OClO dissolved in TFE is interpreted in terms of increased self-association of this solvent relative to ethanol.