The T₁ ← S₀ absorption spectrum of gaseous 4H-pyran-4-thione

The T₁ ← S₀ absorption spectrum of 4H-pyran-4-thione (PT) was measured in a static cell at room temperature (550-620 nm) and in a seeded cold supersonic jet (580-600 nm) using the cavity ring-down (CRD) method. In the static cell absolute extinction coefficients were determined between 573 and 610 nm with an accuracy of ∼±5%. In this region 22 harmonic sequences and 18 hot bands were observed. The energetically lowest ground state vibration at 167.5 cm^-1 was identified as the promoting mode in the static PT gas. The mode in the triplet state was found at 152.3 cm^-1. The CRD absorption spectra of static PT gas and jet-cooled PT are compared with the phosphorescence excitation spectrum of isolated PT. The weak S_1,0 ← S_0,0 absorption was tentatively assigned to a transition at ∼17433 cm^-1.