Photoionization and photoabsorption cross sections of He, O,N2 and O2 for aeronomic calculations

A compilation of experimental and theoretical photoionization and photoabsorption cross sections is presented for He, O, N₂, and O₂ for use in studies of ion and photoelectron production in the terrestrial ionosphere. In wavelength regions where rapid variations occur in the cross sections, averaged cross sections are calculated. When necessary the cross sections have been extrapolated to shorter wavelengths. The cross sections are tabulated at the wavelengths of the solar lines and continua given in the solar reference spectrum of Hinteregger from ～1030 to ～34 Å. For the molecules N₂ and O₂, branching ratios are given for ionization into the ground and electronic states of the molecular ions and for dissociative ionization.