Inelastic scattering of H2CCO ketene induced by He atoms and non-LTE analysis

Abstract

This work deals with the rotational inelastic scattering of ketene (H2CCO) by helium atoms. A new three-dimensional potential energy surface is computed by adopting the explicitly correlated coupled cluster approach with single, double, and perturbative triple excitation [CCSD(T)-F12a] connected to the augmented-correlation consistent-polarized valence triple zeta (aug-cc-pVTZ) Gaussian basis set. A global minimum with a well depth of V = −57.48 cm−1 for (R = 5.93 bohr, θ = 89°, ϕ = 90°) is identified. Quantum scattering calculations involving the 16 lowest states up to JKaKc=817 for ortho form of ketene (o-H2CCO) and the 10 lowest ones up to JKaKc=909 for para form (p-H2CCO) are performed via the close coupling (CC) method up to total energy E = 500 cm−1. Then, rate coefficients are derived for both forms over the temperature range of 5–90 K using the Maxwell–Boltzmann distribution. A predominance of the transitions with ΔJ = ΔKc = 1 for both o-H2CCO and p-H2CCO is obtained. Radiative transfer investigation of excitation and brightness temperatures, as well as optical depth, under non-local thermodynamic equilibrium (non-LTE) conditions for several observed lines is also performed by exploring the determined rate coefficients.