2023MNRAS.522.4038K

Collisional excitation of C₅H⁺ by He was performed by mean of state-of-the-art methods. A high level of theory quantum chemical calculations were made to determine the interaction potential energy surface of C₅H⁺ with helium. The new two-dimensional potential energy surface obtained from the RCCSD(T)-F12 ab initio approach associated with aug-cc-pVTZ basis sets, presents two minima below its dissociation limit with well depths of $-101.8$ and $-100.2\, \mathrm{cm}^{-1}$ . In order to derive accurate physical conditions from rotational transitions of the recently discovered C₅H⁺ molecule in Taurus molecular cloud (TMC-1), rate coefficients calculations are performed. The C₅H⁺(X¹Σ⁺)-He de-excitation rates are obtained after averaging cross-sections for thermal temperature below 100 K. The integral cross-sections are computed with the close-coupling quantum time-independent formalism for $E\le 520 \, \mathrm{cm}^{-1}$ and J ≤ 15. The new collisional data will allow accurate determination of the C₅H⁺ abundance and will help to understand the chemistry of carbon chain ions in the interstellar gas.