Abstract
Fluorescence decays of jet-cooled pyrazine excited at various positions of rovibronic transitions within the 0–0 band were measured by the use of a pulsed dye laser pumped by an excimer or a nitrogen laser. The experimental data thus obtained on the number (N) of the triplet states coupled to the initially excited singlet rovibronic state were analyzed and interpreted by the aid of computer simulation using an asymmetric rotor program. The results indicate that the extraordinarily great variation of N with excitation energy and unreasonably small values of N hitherto reported in the literature can be understood in terms of the conventional theory based on the singlet–triplet mixed state model which has been developed for elucidating the mechanism of the occurrence of dual fluorescence in intermediate case molecules.