The cavity ring-down absorption spectrum of the S0→T1 and S0→S1 transition of jet-cooled 4-H-1-benzopyrane-4-thione

The very sensitive cavity ring-down method has been applied to the measurement of the absorption of 4-H-1-benzopyrane-4-thione (BPT) in a supersonic jet in the wavelength region of the S0→T1 and S0→S1 transition between 15800 and 16650 cm−1. The absorption energies of vibronic states corroborate previous assignments in the multi-photon excitation and S0→T1 phosphorescence excitation spectra of jet-cooled BPT. The symmetry forbidden 0,0 transition, S0,0→S1,0 at 16522 cm−1, was found to be 7.5 times weaker than the absorption transition to the triplet origin, S0,0→T1z,0.