Broadening of the sodium 568.8, 589, 615.4 and 819.4 nm lines by atomic hydrogen

Linewidths and shifts have been calculated in the impact approximation for atomic hydrogen broadening of the Na resonance and 3d-3p, 4d-3p and 5s-3p lines. The S-matrix elements required have been calculated in a time-dependent close-coupling approximation with straight-line paths for each Na term, including fine structure. The NaH potentials were determined using ab initio methods. Allowance was made for possible distant non-adiabatic transitions associated with ionic-covalent avoided crossings in 1Σ+ symmetry. Our result for the width of the resonance line at 5000 K is somewhat below the observed value, although the calculated shift coefficient is consistent with experiment. The shift coefficient for the 615.4 nm (5s-3p) lines is found to be comparable with the broadening coefficient, primarily due to unusual behaviour in the long-range 5s Σ+ potentials. The 819.4 nm (3d-3p) lines are found to have a larger broadening coefficient than the 568.8 nm (4d-3p) lines. For all the multiplets considered the different components of each line have widths differing by no more than a few per cent. Simple empirical fits are provided to the width coefficients of each multiplet.