Structure and spectra of the thioketenyl (HCCS) radical in its ground and first excited states obtained by ab initio coupled-cluster methods

Abstract

There is recent interest in finding the HCCS radical in interstellar sources and a detailed investigation of its UV spectrum has also been reported. By using state of the art coupled-cluster (CC) based ab initio methods, such as coupled-cluster singles and doubles (CCSD) with approximate triple excitation correction (CCSD(T)), the equation-of-motion CC method for excited states (EOMEE-CC) and for ionization potential (EOMIP-CC) together with large basis sets, we present the structure, harmonic vibrational frequencies and dipole moment of the ground and first excited 2Π states. We confirm the experimental rotational constant and most of the assignment made on the vibrational structure of the UV spectrum, but we also suggest reassignments in some cases. Special attention is paid to the Renner–Teller splitting present for such 2Π states.