The excitation of NH2 in the interstellar medium
The excitation of NH2 in the interstellar medium
Résumé
Accurate estimation of the abundance of the NH 2 radical in the interstellar medium requires accurate radiative and collisional rate coefficients. The calculation of hyperfine-resolved rate coefficients for the collisional (de-)excitation of NH 2 by both ortho-and para-H 2 are presented in this work. Hyperfine-resolved rate coefficients are calculated from pure rotational close-coupling rate coefficients using the M j randomizing approximation. Rate coefficients for temperatures ranging from 5 to 150 K were computed for all hyperfine transitions among the first 15 rotational energy levels of both ortho-and para-NH 2 in collisions with ortho-and para-H 2. The new data were then employed in radiative transfer calculations to simulate the excitation of NH 2 in typical star-forming regions such as W31C. We compared the excitation and brightness temperatures for different NH 2 transitions obtained using the new and the previously available collisional data. It is found that the new rate coefficients increase the simulated line intensities. As a consequence, NH 2 abundance derived from the observations will be significantly reduced by the use of the present rate coefficients.
Origine | Fichiers produits par l'(les) auteur(s) |
---|