Electronic energy relaxation of benzophenone vapor

The luminescence of benzophenone vapor at low pressure has been studied as a function of excitation energies as high as the S₂ excitation region, by time-resolved and steady state measurements. At lower excitation energies, emission intensities decayed exponentially, while at higher energies, complex decay curves were obtained that can be analyzed in terms of a biexponential function. The radiative and nonradiative rate constants were determined. The excitation energy dependence of the emission decay rates and quantum yields indicate that only one S-T mixed state is formed by fast intersystem crossing. At least a part of the fast nonradiative process is considered to be the decomposition reaction, which is dominant at higher excitation energies.