Effect of the variation of electric-dipole moments on the shape of pressure-broadened atomic spectral lines

We derive a classical path expression for a pressure-broadened atomic spectral line shape that allows for an electric-dipole moment that is dependent on the position of perturbers. The theory is applied to the atomic hydrogen Lyman-α and Lyman-β lines broadened by collisions with neutral and ionized atomic hydrogen. The far wings of the Lyman series lines exhibit satellites, enhancements that may be associated with quasimolecular states of H₂ and H₂⁺. The sizes of these features depend on the values of the electric-dipole moments at the internuclear separations responsible for the satellites. Profiles are computed with and without spatial dependence of the dipole moment, and are compared with astronomical and laboratory observations. We conclude that in the present case the variation of the dipole moment is an important factor that cannot be neglected.