Line mixing in H broadening of the Na 3P 3D lines

Line mixing of the Na 3P–3D lines broadened by atomic hydrogen has been calculated in the impact approximation. The required S -matrix elements are calculated using a time-dependent close-coupling rectilinear-path approximation, the ab initio NaH potentials used by Leininger et al ( 2000 J. Phys. B: At. Mol. Opt. Phys. 33 1805 ) being employed. At energies of less than 25 000 cm −1 , the real and imaginary parts of the mixing cross sections were found to be about 50 and about 25 times smaller, respectively, than the broadening coefficients, while at about 10 5 cm −1 , the real and imaginary parts were found to be smaller in magnitude by factors of about 200 and 10, respectively. On thermally averaging the cross sections, the line-shape parameters leading to mixing were found to be 50–100 times smaller than the corresponding broadening coefficients for the isolated lines. For a number density of 10 16 – 10 17 cm −3 and temperature of 6000 K, the mixed and unmixed line shapes were found to deviate by less than 3% over the range of frequencies for which the application of the impact approximation was valid.