Reduced rate coefficients D_if for the excitation and de-excitation processes in Na(4s) + H collisions as a function of the electronic bound energy E_f of the final states for the temperature T = 6000 K. The initial bound energy for Na(4s) is E_i = −1.95 eV. The bound energies are measured from the atomic ionization limit. The solid line shows the calculation using the simplified model; symbols show the full quantum calculation (Belyaev et al. 2010; Barklem et al. 2010).