MULTIDIMENSIONAL LEAST-SQUARES RESOLUTION OF RAMAN SPECTRA FROM INTERMEDIATES IN SENSITIZED PHOTOCHEMICAL REACTIONS

摘要

Nonlinear least-squares analysis of transient resonance Raman spectra of a triplet-state photosensitizer (benzophenone) acquired as a function of quencher concentration and laser intensity allows the Raman spectra of the sensitizer excited state and intermediate photoproducts to be resolved from the data. Transient Raman spectra of benzophenone acquired as a function of biacetyl concentration allow a Raman spectrum containing contributions from only the triplet states of benzophenone and biacetyl to be resolved from bands of solvent and ground-state species. The carbonyl stretching frequency of bir acetyl decreases by similar to 580 cm(-1) upon excitation to the triplet state; the rate constant to produce this state by energy transfer from benzophenone triplet state was determined to be k(q) = 2.4 +/- 0.8 x 10(9) L mol(-1) s(-1). A similar analysis of Raman scattering of benzophenone reacting with triethylamine, acquired versus laser intensity and triethylamine concentration, allows the spectra of benzophenone triplet state and its ketyl radical photoproduct to be resolved from each other and from contributions from solvent and ground-state benzophenone bands.