Quantum dynamics of C10H− in the interstellar medium: inelastic collisions with He and formation reaction from the HC10H/H− reactants

Abstract

The anion C₁₀H⁻ is the largest of the linear (C,H)-bearing chains detected so far in the Interstellar Medium. It is therefore important to investigate both possible chemical routes to its formation and the efficiency of it producing rotational excited states via collision with other abundant partners. Here we therefore present and discuss the general features of a new ab initio potential energy surface for the interaction of this linear anion with He and use it to generate its rotationally inelastic quantum collision rate coefficients. Additionally, we carry out a quantum study of the possible formation of the title anion coming from the H⁻ anion reacting with the HC₁₀H neutral precursor, also detected in the same environments. We employ a Legendre Polynomials expansion representation for the purely inelastic interaction while for the reactive process we generate a reduced-dimensionality formulation and employ it within the variational transition state theory (VTST) approach including long-range (LR) corrections. We found that the final inelastic rate coefficients for this anion are all fairly large and that the suggested formation reaction also yields rate coefficients at the cloud's low temperatures which are large enough to be significant, hence to be included within existing chemical networks dealing with polyyne ions formations. The consequences of such findings for the anion's non-equilibrium populations in interstellar environments are discussed in our conclusions.