Quantum Scattering of C3O with para -H2 Collisions under Interstellar Conditions

Carbon-chain molecules, including C3O, found in the interstellar medium (ISM), provide valuable information about the physical conditions, gas dynamics, and evolutionary stages of star-forming regions. Their rotational spectra can serve as sensitive probes of the local gas density and temperature. Interpreting these observations requires accounting for molecular collisions, which influence the rotational states of these species. Because para-H2 is a dominant colliding species in cold molecular clouds, it is essential to calculate the rotational excitation and de-excitation rate coefficients for C3O in collisions with para-H2. For this purpose, the interaction energies between C3O and H2 were computed using the CCSD(T)-F12b/aug-cc-pVTZ level of theory, considering three distinct orientations of the H2 molecule. The interaction energies were further averaged over these orientations to obtain the truncated two-dimensional potential energy surface (PES), which exhibits a minimum of −128.3 cm–1 at R = 3.3 Å. The quantum time-independent close-coupling (CC) calculations for C3O with para-H2 collisions included the first 51 rotational levels and collision energies up to 1025 cm–1. The rate coefficients were obtained for temperatures from 1 to 150 K by averaging the cross-sections over a Maxwell–Boltzmann distribution of kinetic energies. These results provide a good approximation for C3O with para-H2 (j2 = 0) collisions and are found to be much larger in magnitude for weaker transitions when compared with the C3O–He system. The calculated rate coefficients are expected to assist in making reliable estimates of C3O abundances in non-local thermodynamic equilibrium (LTE) conditions present in the ISM.