THIOFORMALDEHYDE SINGLE ROTATIONAL LEVEL PHOTOPHYSICS - LONGER THAN RADIATIVE LIFETIMES AND REDUCED FLUORESCENCE YIELDS IN THE ISOLATED MOLECULE

Single rotational level fluorescence lifetimes and relative fluorescence quantum yields have been measured under collision-free conditions for a variety of rotational levels in the 41 vibrational state of S1 H2CS. About half of the rotational levels studied decay with a radiative lifetime of ≈ 170 μs. Other levels decay with lifetimes longer than the radiative lifetime and these states correlate with perturbations observed in the spectrum, as detected by Doppler-limited laser-induced fluorescence and sub-Doppler intermodulated fluorescence techniques. The levels coupled to T1 and most of the levels coupled to S0 have relative fluorescence yields near unity. A few levels in S1 show reduced quantum yields of fluorescence which persist at pressures as low as 5×10-7 Torr. A sequential coupling model is proposed to qualitatively account for the observed excited state dynamics of these levels. © 1990 American Institute of Physics.