Temperature dependence of rotational excitation rate coefficients of C2H− in collision with He

From a new two-dimensional Potential Energy Surface (PES), rotational excitation of the C2H−(X1Σ+) anion by collision with He is investigated. PES is obtained in the supermolecular approach based on a single and double-excitation coupled cluster method with perturbative contributions from triple excitations (CCSD(T)). quantum close-coupling calculations of inelastic integral cross sections are done on a grid of collision energies large enough to insure converged state-to-state rate coefficients for the 13 first rotational levels of C2H− and temperatures ranging from 5 to 100 K. For this collisional system, rate coefficients exhibit a strong propensity in favor of even ΔN transitions.