Ab initio calculations on the X∼B → X∼A photoelectron spectrum of thioformaldehyde negative ion.

The equilibrium structures, multidimensional potential energy surfaces, and anharmonic vibrational frequencies of thioformaldehyde (HCS) and its B radical anion were obtained at the (U)CCSD(T)-F12a/cc-pVTZ-F12 level; and the photoelectron spectrum of HCSX∼B→ HCS X∼A was simulated by calculating the Franck-Condon factors (FCFs). The additional electrons cause a significant change in the bond length of the C = S bond of HCS, which affects the potential energy surface and the C = S bond stretching mode, while the interaction between electrons turns the originally planar structure of HCS into a slightly out-of-plane umbrella structure, resulting in an unusual change in the vibrational frequency of the out-of-plane bending mode. Finally, a time-independent eigenstate-free Raman wave function approach (RWF) was used to calculate the photoelectron spectrum of HCS and to point out the changes in the band under the influence of different temperatures. These data provides a theoretical basis for interstellar observations and experimental studies.