ROTATIONAL EFFECTS ON SINGLET-TRIPLET INTERACTION OF P-BENZOQUINONE VAPOR

Fluorescence decays are observed following excitation at the individua l rotational lines of the 0(0)0, 22(0)1, and 26(0)1 vibronic bands bel onging to the S0 --> B-1(1g)(npi) transition. With excitation at the 22(0)1 and 26(0)1 bands, fluorescence lifetime varies remarkably along the rotational contour. A comparison between the fluorescence excitat ion spectra and simulated spectra suggests that the fluorescence quant um yield decreases with increasing J' of the excited level. The rotati onal state dependence of both the yield and lifetime of fluorescence a t 22(1) and 26(1) of S1 is interpreted in terms of the K scrambling in the triplet manifold reached via the intersystem crossing. With excit ation into the vibrationless level, on the other hand, the lifetime is independent of the excited rotational level and the fluorescence exci tation spectrum well agrees with the simulated absorption spectrum, im plying that singlet-triplet interaction is extremely weak at the B-1(1 g) origin.