Investigation of rotational (de-)excitation of cyanic acid (HOCN) by collision with He atoms

ABSTRACT The rotational inelastic (de-)excitation of the cyanic acid (HOCN) molecule by collision with helium (He) atoms is studied. A new three-dimensional potential energy surface (3D-PES) for the HOCN−He van der Waals system is given. Explicitly correlated coupled cluster approach with single, double and perturbative triple excitation (CCSD(T)-F12a) in conjunction with augmented-correlation consistent-polarized valence triple zeta (aVTZ) Gaussian basis set is adopted to generate the ab initio 3D-PES. A global minimum with a well depth of 87.59 cm−1 localized at R = 5.9 bohr, θ= 76°, ϕ = 90° is found. Rotational inelastic cross-sections relevant to the 21 first rotational levels (up to $J_{K_aK_c}=8_{08}$) are investigated for total energy up to 550 cm−1 using coupled-states approach. Thermal rate coefficients are obtained for temperatures ranging between 0 and 90 K. |ΔJ| = 1 with |ΔKa| = |ΔKc| = 0 processes are found to be the predominant ones.