Modelling rotational state changes in C3N− and CN− by collision with H in interstellar environments

ABSTRACT The anions CN$^-$ and C$_3$N$^-$, both as $^1 \Sigma _{\rm g}^+$ electronic states, are among the oldest of the (C,N)-bearing linear anions discovered in the dark cloud core, TMC-1, more than 15 yr ago. They are also interesting species to be studied in cold trap conditions that can mimic those temperature ranges that are dominant in the astrophysical environments. The hydrogen atoms and molecules are the most abundant neutral species in those same environments, and therefore, it is important to be able to have reliable information on their collision efficiency in driving the previous anions to different populations of their internal rotational states. In this study, we devise a way of focusing the ab initio calculations of the anions’ interactions with H atoms primarily on the inelastic, energy-transfer channels and, therefore, are able to generate the corresponding rotationally inelastic rate coefficients at temperatures between 10 and 220 K. The results from such findings could help us to clarify possible experimental data in traps and also allow us to establish the substantial efficiency of this atomic partner in causing collision-driven rotational state changes at low temperatures for the present anions of the interstellar medium environments.