Rotational Excitation of the CP(X2Σ+) Open Shell Molecule Due to Collision with He(1S)

Phosphorus bearing molecules have been discovered in the circumstellar and interstellar media. Modeling their abundance accurately requires computations of rate coefficients induced by collision with He and H-2 (i.e., the most abundant gaseous components). These calculations may be carried out by first determining highly accurate potential energy surface (PES) and cross sections. In this paper, we present the first PES of the CP(X-2 Sigma(+))-He(S-1) van der Waals collisional complex. The ab initio interaction potential was performed using the explicitly correlated restricted coupled cluster approach with simple, double, and perturbative triple excitation (RCCSD(T)-F12) in connection with the augmented-correlation consistent-polarized valence triple-zeta Gaussian basis set (aug-cc-pVTZ). The potential presents two minima of -18.62 cm(-1) and -18.72 cm(-1). From the PES obtained, we have computed state-to-state excitation cross sections of CP due to collision with He for energies up to 500 cm(-1). Rotational transitions involving the fine-structure levels of the CP molecule were treated with a recoupling technique based on the scattering matrix calculated with the exact quantum mechanical close coupling method. Discussions on the propensity rules between the fine-structure levels were made and we found that the Delta j = Delta N transitions are favored with respect to the Delta j not equal Delta N ones. The data presented in this paper may have a great impact on the accurate determination of the CP abundance in space.