Effects of Molecular Vibration and Rotation on Intramolecular Dynamics in S1 of s-Triazine Vapor

Emission properties of s-triazine vapor have been examined for excitation into various vibronic levels of S1. The emission involves broad fluorescence besides the sharp fluorescence emitted from the initially prepared vibronic level (IPL). At low pressures, the IPL fluorescence exhibits a biexponential decay composed of fast and slowly decaying portions, and the broad fluorescence also consists of fast and slow components with lifetimes comparable to those of the IPL fluorescence. The broad fluorescence exhibits another slow component, which is characterized by a less tendency to undergo collisional quenching. The emitting levels of the broad fluorescence are regarded as reached directly from the IPL and indirectly via triplet state. The quantum yield of the slow component of the IPL fluorescence remarkably depends on the rotational level excited, whereas the quantum yield of the broad fluorescence is nearly independent of the rotational level excited. These results suggest that K scrambling occurs not only in the intersystem crossing between singlet and triplet levels but also in the relaxation to other singlet levels from the IPL.