The phosphorescent state of pyrazine has been studied with theT → Semission andT ← Sexcitation methods in combination with microwave techniques in the systems of pyrazine-h4in pyrazine-d4, pyrazine-h4and -d4inp-dioxane,p-xylene, and benzene, and pyrazine-h4x-trap. The three out-of-plane hydrogen bending vibrations ofv10a,v5andv17aare found to be active in theTxsublevel emission of the isotopic mixed crystal. By modifying the force constants used by Scully, the frequencies of the out-of-plane vibrations were reexamined and the result was compared with the observed frequencies.