Electronic Energy Relaxation in Toluene Vapor

Abstract

Fluorescence and crossover to the triplet state are the only important relaxation paths for toluene excited to the lowest vibrational level of the first singlet state. The fluorescent yield at 2668Å is 0.30 ± 0.07 and this is zero at 2400 Å. The triplet yield (Cundall method) is 0.70 ± 0.03 at 2668 Å and is lower at shorter wavelengths. Probably fluorescence and crossover to the triplet state occur only from the vibrationless level of the upper singlet state under the experimental conditions used. Some other process must become important at short wavelengths, and this process competes successfully with vibrational relaxation. Fluorescence of toluene is quenched by krypton and xenon presumably because of collision‐induced crossover to the triplet state.