Rotational effects on fluorescence yields and decays from the lower vibronic levels of the S 1 state of s-triazine vapor

Abstract

Fluorescence quantum yields and decays of s-triazine vapor have been measured at different excitation positions along the rotational contours of the 6 0 1 and 6 0 2 absorption bands and at different pressures (40 mTorr-200 Torr). The characteristics of the fast fluorescence component are roughly independent of the rotational level excited, while those of the slow component show a marked rotational level dependence. The slow fluorescence quantum yield gives a sharp peak near the band origin, where the corresponding lifetime exhibits a distinct minimum. These results are related to the observation that the density (or number) of triplet levels coupled to the optically prepared singlet level increases with increasing total rotational angular momentum quantum number, J′. The slow component is efficiently quenched by long-range collisions, indicating that as a result of collision-induced relaxation the molecule is transferred from the S-T mixed rovibronic level mainly to the pure triplet rovibronic manifold.