Laser-induced fluorescence and pure rotational spectroscopy of the $CH2CHS$ (vinylthio) radical

Laser-induced fluorescence (LIF) excitation spectra of the $B̃–X̃A″2$ electronic transition of the $CH2CHS$ radical, which is the sulfur analog of the vinoxy $(CH2CHO)$ radical, were observed under room temperature and jet-cooled conditions. The LIF excitation spectra show very poor vibronic structures, since the fluorescence quantum yields of the upper vibronic levels are too small to detect fluorescence, except for the vibrationless level in the $B̃$ state. A dispersed fluorescence spectrum of jet-cooled $CH2CHS$ from the vibrationless level of the $B̃$ state was also observed, and vibrational frequencies in the $X̃$ state were determined. Precise rotational and spin-rotation constants in the ground vibronic level of the radical were determined from pure rotational spectroscopy using a Fourier-transform microwave (FTMW) spectrometer and a FTMW-millimeter wave double-resonance technique [Y. Sumiyoshi et al, J. Chem. Phys. 123, 054324 (2005)]. The rotationally resolved LIF excitation spectrum for the vibronic origin band of the jet-cooled $CH2CHS$ radical was analyzed using the ground state molecular constants determined from pure rotational spectroscopy. Determined molecular constants for the upper and lower electronic states agree well with results of ab initio calculations.