Collisional excitation rate coefficients of N2H+ by He

Fabien Daniel (1) , Marie-Lise Dubernet-Tuckey (1) , Markus Meuwly (2) , José Cernicharo (3) , Laurent Pagani (1)

1 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
2 Unibas - Université de Bâle = University of Basel = Basel Universität
3 DAMIR/CSIC - Department of Molecular and Infrared Astrophysics, Consejo Superior de Investigaciones Científicas

Using a recoupling technique with close-coupling spin-free calculations de-excitation rate coefficients are obtained among hyperfine transitions for He colliding with N₂H⁺. A recently determined potential energy surface suitable for scattering calculations is used to investigate rate coefficients for temperatures between 5 and 50 K, and for the seven lowest rotational levels of N₂H⁺. Fitting functions are provided for the Maxwellian averaged opacity tensors and for the rotational de-excitation collisional rate coefficients. The fitting functions for the opacity tensors can be used to calculate hyperfine (de)-excitation rate coefficients among elastic and inelastic rotational levels, and among the corresponding magnetic sublevels of the hyperfine structure. Certain dynamical approximations are investigated and found to be invalid.

Domaines: Astrophysique [astro-ph]

Fabien Daniel, Marie-Lise Dubernet-Tuckey, Markus Meuwly, José Cernicharo, Laurent Pagani. Collisional excitation rate coefficients of N2H+ by He. Monthly Notices of the Royal Astronomical Society, 2005, 363, pp.1083-1091. ⟨10.1111/j.1365-2966.2005.09542.x⟩. ⟨hal-03733247⟩