Long fluorescence lifetime of pyrazine vapors

By the study of the pressure dependence of the fluorescence and phosphorescence yields of pyrazine vapors in the pressure range of 10⁻²-10 torr it was established that the fluorescence decay is not exponential but contains a long component (τ ≈ 10⁻⁶–10⁻⁷ sec) corresponding to the “dilution” of the singlet radiative properties in the dense manifold of triplet levels. The phosphorescence is due exclusively to the collisionally induced relaxation from the quasi-stationary state to the pure triplet state.