Ab initio calculation of the transfer and multipole rates of the Na ground state hyperfine levels perturbed by atomic hydrogen

A theoretical treatment of the multipole relaxation and transfer rates due to isotropic collisions is presented. Explicit expressions are obtained for the collisional rate constants of the hyperfine-structured ground level of the Na I atoms perturbed by collisions with H atoms. As the effects of Na nuclear spin during the collision are negligible, it is shown that all the rate constants involve the same electronic relaxation rate of the multipole of rank one. Evaluation of these rates has been carried out using very accurate potential energy curves.The formulae given here for the depolarizing collisional rates should be useful for accurately modeling the complex linear polarization pattern of the Na I doublet that can be observed in quiet regions of the solar atmosphere using spectro-polarimeters of high polarimetric sensitivity.