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On the gas-phase formation of the HCO radical : accurate quantum study of the H+CO radiative association

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Authors : Thierry Stoecklin, Philippe Halvick, Hua-Gen Yu, Gunnar Nyman, and Yves Ellinger
Abstract : We present the first quantum study of the radiative association of H and CO to form the HCO molecule within a time-independent approach.We use a recently published 3D potential energy surface of spectroscopic accuracy and two 3D dipole moment surfaces, which were calculated for this study. We discuss the variation of the radiative association cross-section as a function of
both the rotational angular momentum of CO and the total angular momentum and use the uniform J-shifting approach to obtain the global radiative association rate coefficient. The effect of the saddle point separating the HCO molecule from the H+CO reactants and the main features of the radiative association cross-sections are analysed and discussed. The calculated rate coefficient is below 10−23 cm3 molecule−1 s−1 for temperatures lower than 30 K, and increases up to 5 × 10−20 cm3 molecule−1 s−1 at T = 300 K. These results demonstrate that the gas-phase H+CO radiative association cannot be the process at the origin of the sequence leading to the formation of methanol in a cold interstellar medium