Potential energy surface and low-temperature rate coefficients of cyano thioformaldehyde (HCSCN) by collision with helium (He)

Molecular collisional data are essential for accurately modeling molecular abundances and excitation in the interstellar medium (ISM), yet remain scarce for many sulfur-bearing species. In this work, we calculate collisional rate coefficients for the near-prolate asymmetric top molecule HCSCN in collision with helium. A highly accurate three-dimensional potential energy surface (PES) was constructed at the CCSD(T)-F12a/aug-cc-pVTZ level of theory. Utilizing this PES, we performed coupled state calculations of inelastic cross sections for rotational transitions between the first 71 rotational levels with energies below 20 cm−1 and collisional energies up to 500 cm−1, from which we derived collisional rate coefficients up to 100 K. The calculated PES is highly anisotropic, exhibiting numerous minima with the deepest value being 53 cm−1 at certain positions in and out of the HCSCN molecule plane. The collisional rates obtained for the b-type transitions are of the same magnitude as those of a-type transitions, with a slight inferiority. The rotational relaxation rate coefficients have a propensity rule that favors |ΔJ| = 1, |Δka| = |Δkc| = 0 for a-type transitions, while ΔJ = 0, |ΔKa| = |ΔKc| = 1 for b-type transitions. These data provide important insights into sulfur chemistry in the ISM and will aid in more accurate modeling of molecular abundances in environments such as TMC-1.