Rotational de-excitation of tricarbon monosulfide (CS) in collision with (He): potential energy surface and rates

Despite that the tricarbon monosulfide (CS) is among the first sulfur-containing carbon-chain molecules to be detected in the interstellar medium, no studies focused on the determination of its collisional rates. These rate coefficients are essential to estimate the abundance of CS in the interstellar medium. Computations of the CS(Σ+1) downward rate coefficients, induced by collision with He, are performed by averaging the integral cross sections at low temperature (below 25K). Calculations of the cross sections in the close-coupling quantum time independent formalism for Ec≤110cm−1 and J≤ 10 are based on a new 2-D potential energy surface. This PES is obtained from the explicit correlated coupled cluster with a single, double and perturbative triple excitation [ccsd(t)-f12] ab initio approach and the aug-cc-pVTZ basis sets. The PES have a global minimum of −55.69cm−1 located at R= 6.25 bohr and θ= 94 , and a second minimum of −36.95cm−1 at R= 9.35 bohr and θ= 0 . A comparison of CS rates with those of the isoelectronic molecule CO was made. The results indicate a great temperature dependence of the rates for transitions of Δ J> 2. We expect that the new collisional data will allow for accurate determination of the CS abundance in several interstellar regions.