A theoretical study of the low-lying excited electronic states of thiocarbonyl chlorofluoride and their dissociation pathways.
The spectroscopic constants for the ground (X (1)A(1)) and low-lying triplet and singlet excited states (a (3)A("),A (1)A("),B (1)A(')) of thiocarbonyl chlorofluoride (ClFCS) were obtained using the equation-of-motion coupled-cluster singles and doubles method. The calculated vibrational frequencies of the electronic states were within 4% of the experimental values for 21 of the frequencies, but four calculated frequencies were 20%-40% away from the corresponding experimentally reported values, suggesting the need to reexamine previous experimental spectra. The spectroscopic properties of the radical fragments (FCS, ClCS, and CClF) were also studied, and the correlation diagram between the excited electronic states of ClFCS and possible combinations of dissociation fragments were obtained. The potential energy surfaces (PESs) of the excited electronic states of ClFCS along possible dissociation pathways were also studied. The main qualitative dynamical features of the S(1)(A (1)A("))<--S(2)(B (1)A(')) fluorescence of ClFCS, which may occur in spite of the small barrier (8 kcalmol) on the S(2) PES to the dissociation of C-Cl bond, are discussed.