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

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Abstract From a new two-dimensional Potential Energy Surface (PES), rotational excitation of the C 2 H − (X 1 Σ + ) 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)). Fully-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 C 2 H − and temperatures ranging from 5 to 100 K. For this collisional system, rate coefficients exhibit a strong propensity in favor of even Δ N transitions.