Fluorescence Lifetime of Benzene and Benzene-d6 Vapor Excited to Single Vibronic Levels

Abstract

The fluorescence decay curves and lifetimes of benzene and benzene‐d 6 vapor have been determined for excitation to each of several low‐lying single vibronic levels of the 1 B 2u state. Measurements were made at pressures as low as 0.1 torr, where the benzene system is essentially collision free, and at higher pressures of both benzene and benzene plus an added thermalizing gas. The lifetime was found to vary with the vibrational level acting as the origin for emission. The variation of the radiative lifetime with vibronic level was consistent with the predictions of Herzberg–Teller Theory for vibronically induced transition. In addition, there appears to be a deuterium isotope effect on the nonradiative decay processes. The fluorescence lifetimes obtained permit a re‐examination of some of the steady‐state data in the literature pertaining to the variation of the quantum yield of fluorescence with pressure. Also, inefficient electronic quenching is found when isopentane is used as a thermalizing gas.