Rotational state-changing collisions of C₂H⁻ and C₂N⁻ anions with He under interstellar and cold ion trap conditions: A computational comparison

We present an extensive range of quantum calculations for the state-changing rotational dynamics involving two simple molecular anions that are expected to play some role in the evolutionary analysis of chemical networks in the interstellar environments, C₂H⁻ (X¹Σ⁺) and C₂N⁻ (X³Σ⁻), but for which inelastic rates are only known for C₂H⁻. The same systems are also of direct interest in modeling selective photo-detachment experiments in cold ion traps where the He atoms function as the chief buffer gas at the low trap temperatures. This study employs accurate, ab initio calculations of the interaction potential energy surfaces for these anions, treated as rigid rotors, and the He atom to obtain a wide range of state-changing quantum cross sections and rates at temperatures up to about 100 K. The results are analyzed and compared for the two systems to show differences and similarities between their rates of state-changing dynamics.