Rotational cross sections and rate coefficients of $\mathrm{CP}(\mathrm{X}^{2}\varSigma ^{+})$ induced by its collision with $\mathrm{He}(^{1}S)$ at low temperature

Abstract

The potential energy surface (PES) for the $\mathrm{CP}(\mathrm{X}^{2}\varSigma^{+})$-$\mathrm{He}(^{1}S)$ complex has been calculated at the RCCSD(T)-F12/VTZ-F12 level of theory. The analytic fit of the PES was obtained by using global analytical method. The fitted PES was used subsequently in the close-coupling approach for the computation of the state-to-state collisional excitation cross sections of the fine-structure levels of the CP-He complex. Collision energies were taken up to 1500 cm⁻¹ and they yield after thermal averaging, state-to-state rate coefficients up to 200 K. The propensity rules between the lowest fine-structure levels were studied. These rules show, on one hand, a strong propensity in favour of even $\Delta N$ transitions, and the other hand, that cross sections and collisional rate coefficients for $\Delta j =\Delta N$ transitions are larger than those for $\Delta j\neq \Delta N$ transitions.