Spectroscopic Constants and Anharmonic Force Field of Thiocarbonyl Thioketen and its Isomers: a Theoretical Study

The interstellar medium molecule thiocarbonyl thioketen, H₂CCS, has several stable isomers and has received considerable attention of astronomical observation in recent years. The positions of H, C, and S atoms of three isomers lead to diverse dipole moments and spectroscopic constants. The anharmonic force field and spectroscopic constants of thiocarbonyl thioketen and its isomers are calculated using MP2, B3LYP, and CCSD(T) methods employing correlation consistent basis sets. Molecule structures, rotational spectroscopic constants, and fundamental frequencies are compared with the available experimental data for thiocarbonyl thioketen. Ro-vibrational interaction constants, anharmonic constants, cubic and quartic force constants are predicted for thiocarbonyl thioketen. In addition, some rotational and vibrational spectroscopic parameters are predicted with the same level of theory for thioacetylene, HCCSH, and thiirene, (CH)₂S. The predictions of these spectroscopic constants are expected to guide the future astronomical observation and high resolution experimental work for C₂H₂S isomers.