Theoretical study of low-lying excited states of X2CY (X = F, Cl; Y = O, S) using the equation-of-motion coupled-cluster theory

Abstract

The spectroscopic constants of the ground ( ) and low-lying excited states ( ) of Cl2CS, F2CS Cl2CO and F2CO were studied using the coupled-cluster and the equation-of-motion coupled-cluster singles and doubles (CCSD/EOM-CCSD) method. A comparison of the calculated results for Cl2CS with available experimental values shows that the results from the CCSD/EOM-CCSD method are quite reliable. Many other spectroscopic constants of the excited states of the four molecules are provided in this work. It is shown that the fluorescence corresponding to the S2→S1/S2→S0 transition is also expected in F2CS and F2CO as well as in Cl2CS, an already known violation of Kasha's rule.