Dynamic Behavior of Individual

Pulsed Doppler-free two-photon excitation of Single rotational states o f the 141 vibronic State of benzene with a resolution of 70 M H z is employed to investigate the influence of molecular rotation on the decay behavior o f these states. The analysis of the completely resolved (Av = 15 M H z ) spectrum o f the 14J band, measured with a C W laser, makes it possible to specify whether ind i v idua l states are perturbed by other ("dark") Sj states and allows the precise determination of the degree of admixture of these background states. The vibrat ional identity o f the background states is known from emission spectra of Single rov ibronic states. Unperturbed rovibronic states were investigated up to J'K> = 6 7 6 l , and a pure exponential decay was found which does not depend on molecular rotation in accord with a nonradiative decay of S, benzene in the Statistical l imi t . The decay o f perturbed states, which was also found to be purely exponential, depends strongly on the degree of admixture of the background State and on its v ibrat ional identity. Values of the decay time of two identified " da rk " zero-order S, v ibrat ional states, which cannot be directly excited by opt ical transitions, are determined by evaluation o f the decay behavior of the perturbed states.