A spectroscopic study of fluorescence from the second excited singlet state of thiophosgene vapor

Abstract

The S₂–S₀ absorption, emission, and excitation spectra of thiophosgene vapor have been measured and the observed single vibronic transitions assigned. Comparison of the absorption and excitation spectra reveals that emission is excited only when transitions to the upper state terminate in 3^m4ⁿ, m or n=0 or 1, and that the upper state is depopulated by rapid radiationless processes when higher vibrational levels are populated. The most prominent bands in the emission spectrum are those in which the transitions terminate in 1_p3_q4_r with 1⩽p⩽10, 1⩽q⩽5, and 1⩽r⩽4. All three types of spectra are consistent with a pyramidal excited state in which the equilibrium internuclear distances are substantially greater than those of the ground state. The implications of this fluorescence ’’anomaly’’ with respect to the nature of radiationless processes in the thiophosgene are discussed.