Scattering calculation of the newly observed pentacarbon monoxide (C5O) with He atom: de-excitation rates and radiative transfer

Abstract

ABSTRACT To determine the chemical composition of gases in molecular clouds, the oxygen-bearing systems CnO are needed as probe elements. The pentacarbon monoxide C5O was recently detected in TMC-1, and in order to derive accurate physical conditions from its rotational transitions, calculation of rate coefficients of C5O(1Σ+) induced by collision with He are performed for thermal temperature below 100 K. These calculations are based on a new 2D potential energy surface (2D-PES) obtained from the explicit correlated coupled cluster with single, double, and pertubative triple excitation (ccsd(t)-f12) ab initio approach associated with aug-cc-pVTZ basis sets. The C5O–He PES presents two minima below its dissociation limit with a well depths of −59.321 and −53.059 cm−1. By mean of this PES, the integral cross sections are calculated in the close-coupling quantum time independant formalism for $E\le 500 \, {\rm cm}^{-1}$ and J ≤ 20. The de-excitation rate coefficients are obtained after averaging these cross sections at low temperatures. We expect that the new collisional data will allow accurate determination of the C5O abundance in the interstellar medium, as well as the interpretation of its emission lines. These new data are crucial to understand the chemistry of carbon chain species in the interstellar gas.