Ionization of an exponential atmosphere by monochromatic solar radiation is considered when the recombinance α is not independent of height but varies as α₀ + α₁e^-bh, where α₀, α₁ and b are constants. A recombinance datum level is defined, namely the level where α₀ and α₁ e^-bh are equal: heights are measured from this level, in scale-height units. The level of the absorption peak being z_x. (when the sun's zenith distance is χ, or z₀ when χ = 0), the level zm of the electron peak and the height distribution of the electron density n_e are considered, for different values of z₀ and of c(=b/H), particularly c = 1, 2, 3. When c > 0 the electron peak is always above the absorption peak, and for c gt-or-equal, slanted 2 it is always above the recombinance datum level: the electron peak for c=1, when the absorption peak is below the recombinance datum level, is about half way between the two. The decrease of n_e (from its maximum value n_em) on the underside (or incline) of the electron layer can be much less steep than for a Chapmanlayer, if the absorption peak is below the recombinance datum level.

The results for the model atmospheres considered are tentatively discussed with reference to the E and D ionospheric regions, but their potential value may be realized only when better data for the D region become available.