A theoretical study of the low-lying excited electronic states of thiocarbonyl chlorofluoride and their dissociation pathways

Abstract

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.

Predissociative T1and S1states of carbonyl chlorofluoride (ClFCO) and their photodissociation pathways

“…The differences between the second and third columns, therefore, correspond to the possible effects of the frozen-core MOs on the geometries and vibrational properties; it is clear that the effects are negligibly small, as explicitly demonstrated in many previous cases [24,25,[35][36][37]. The differences between the third and fourth (CCSD(T)/6-31þG(d)) columns indicate the size and trend of the possible effects of higher-order excitations on the results of the electron-correlation methods: the changes in the bond lengths, bond angles, and vibrational frequencies due to the inclusion of non-iterative triples in the CCSD(T) method are less than 0.006 Å , 0.1 , and 2%, respectively.…”

“…Note that the values for thiocarbonyl chlorofluoride (ClFCS) are much smaller, 2041 (T 1 ) and 1556 cm À1 (S 1 ), respectively, because the C-S bond is longer than the C-O bond [25]. The normal-mode displacement vectors of the harmonic vibrations of the T 1 and S 1 states are shown in the second and third rows of Figure 1, respectively.…”

“…The geometries and excitation energies of the lowest triplet (T 1 ) state and the first excited singlet (S 1 ) state have been reported very recently [19,23], but no further details of the vibration frequencies and the PESs of any possible dissociation paths of the excited electronic states have previously been provided. Even our recent theoretical studies of the low-lying excited states of tetra-atomic halocarbonyls X 2 CY (X ¼ F, Cl; Y ¼ O, S) [24] and ClFCS [25] did not include ClFCO. The lack of reliable theoretical information on the excited electronic states of ClFCO means that previous experimental studies [12,21,22] of the photodissociation of ClFCO have been analysed only phenomenally, and that very few details of its ultrafast dynamics have emerged.…”