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Approximations in Brueckner's theory of spectral line broadening by collisions with neutral hydrogen atoms relevant to a solar-type atmosphere are discussed, and a modified theory for s-p transitions is presented. The theory utilizes explicit expressions for the interatomic interaction energy between a hydrogen atom in its ground state and general m=o, + or - 1 p states, derived from second-order perturbation theory without exchange, allowing the removal of the Lindholm-Foley average over m states in the original Brueckner model. Approximate upper and lower bounds for the linewidth of the sodium D lines are derived, and these values are contrasted with available theoretical, experimental and solar empirical results. The removal of the Lindholm-Foley average is shown to reduce the D-state linewidths by about 30 percent, and an analysis of the interatomic separations important in the line broadening cross-section for the D lines has shown that there is little atomic overlap at the separations that are important.
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