Theoretical and laboratory spectra of sodium perturbed by molecular hydrogen^⋆

¹ GEPI, Observatoire de Paris, UMR 8111, CNRS, Université Paris VII, 61 avenue de l’Observatoire, 75014 Paris, France
e-mail: nicole.allard@obspm.fr
² Institut d’Astrophysique de Paris, UMR 7095, CNRS, Université Paris VI, 75014 Paris, France
³ Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA
⁴ Laboratoire de Chimie et Physique Quantique, UMR 5626, CNRS, Université Paul Sabatier, 118 route de Narbonne, 31400 Toulouse, France
⁵ Department of Physics and Astronomy, University College London, Gower Street, WC1E6BT London, UK

Received: 14 February 2012
Accepted: 17 May 2012

Abstract

We present new unified theory line profiles of neutral Na perturbed by H₂. We used a priori Na–H₂ potentials, transition dipole moments and validated pseudo-potentials as input to the line shape, and evaluated the profiles for temperatures and densities appropriate for modeling exoplanet and brown dwarf atmospheres. The theory for the resonance lines was compared with new laboratory spectra of sodium to test the validity of the potentials and resulting profiles. The Lorentzian function commonly used to approximate a collisional line profile in radiative transfer calculations is shown to be inadequate, except within a few halfwidths of the line center. In the far wing, the opacity caused by collisions may be several orders of magnitude greater than the extrapolation of the Lorentzian core.