Rotational (de)-excitation of linear C3O by collision with He

Abstract

Tricarbon monoxide (C₃O) is an astrochemically important molecule. It is a probe element for determining the chemical composition of gases in molecular clouds, as C₃O is a major intermediate of ion-molecule reactions in the gas phase. For C₃O, no collision coefficients are available in the literature. To estimate the abundance of C₃O in a solar cold dark cloud: Taurus Molecular Cloud 1 (TMC-1) and find the range of cloud parameters, some authors used the calculated values for the HC₃N molecule, which is isoelectronic and has similar rotational constants. Indeed, the calculation of the rate coefficients of C₃O(¹Σ⁺) induced by collision with He is performed for thermal temperatures below 25 K. These calculations are based on a new two-dimensional potential energy surface obtained from the explicitly correlated coupled cluster with a single, double and perturbative triple excitation (ccsd(t)-f12) ab initio approach associated with aug-cc-pVTZ basis sets. The PES was found to have a global minimum at (R = 6.2 Bohr and θ = 73°) with a depth of −53.4 cm⁻¹ below the C₃O–He dissociation limit. Using this PES, the integral cross sections are performed in the close-coupling quantum time independant formalism for E_c ≤ 110 cm⁻¹ and J ≤ 12. These cross sections were then averaged at low temperature to obtain the downward rate coefficients. The new collisional data should significantly help the interpretation of interstellar C₃O emission lines observed with current and future telescopes. We expect that they will allow the accurate determination of the C₃O abundance in the interstellar medium, which is crucial to understand the chemistry of carbon chain species in the interstellar gas.