Dynamic Behavior of Individual Rovibronic States in S₁ Benzene

Abstract Pulsed Doppler‐free two‐photon excitation of single rotational states of the 14 1 vibronic state of benzene with a resolution of 70 MHz is employed to investigate the influence of molecular rotation on the decay behavior of these states. The analysis of the completely resolved ( Δv = 15 MHz) spectrum of the 14 1 0 band, measured with a CW laser, makes it possible to specify whether individual states are perturbed by other (“dark”) S 1 states and allows the precise determination of the degree of admixture of these background states. The vibrational identity of the background states is known from emission spectra of single rovibronic states. Unperturbed rovibronic states were investigated up to J' K' = 67 61 , and a pure exponential decay was found which does not depend on molecular rotation in accord with a nonradiative decay of S 1 benzene in the statistical limit. The decay of perturbed states, which was also found to be purely exponential, depends strongly on the degree of admixture of the background state and on its vibrational identity. Values of the decay time of two identified “dark” zero‐order S 1 vibrational states, which cannot be directly excited by optical transitions, are determined by evaluation of the decay behavior of the perturbed states.