Calculated potentials for the NaHe molecule are used to obtain collision-induced widths and shifts for the sodium D lines together with cross sections for fine-structure transitions and the relaxation of the multipole polarizations of the resonance levels. The atomic collision is treated in an adiabatic approximation in which the colliding atoms form a molecular system which rotates during the collision. We find the resonance lines to be broadened equally and to be approximately 70% wider, and with associated shifts of an order of magnitude smaller, than expected on the basis of van der Waals forces. The dependence of the cross sections for relaxation of the multipole polarizations of the resonance levels on the molecular-coupling conditions and the rotation of the system during collision is discussed and indicates a limitation on the sum rule for these cross sections. Good over-all agreement with the existing experimental data is obtained.

A collection of some 700 experimental D-region electron density profiles has been digitized and made easily computer accessible. By using these profiles the density at a given height has been determined and modeled as a function of solar zenith angle, sunspot number, latitude, season, and magnetic index. Expressions have been obtained for the density at heights from 55 to 90 kin. It is found that the effects of the different parameters of the model vary with height. Magnetic effects, for example, are more important above 80 km, while latitude effects are most important at 60 km.

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