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

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, theta = 76 degrees, phi = 90 degrees is found. Rotational inelastic cross-sections relevant to the 21 first rotational levels (up to J(KaKc) = 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. vertical bar Delta J vertical bar = 1 with vertical bar Delta K-a vertical bar = vertical bar Delta K-c vertical bar = 0 processes are found to be the predominant ones.