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One of the important problems of upper atmospheric and astrophysical research is the determination of the frequencies of collisions between electrons and atomic systems. Informa tion on this subject can be obtained from a knowledge of the total cross-section, Q, and to some extent from the differential cross-section, (hg), of the collision. The temperatures at which these collisions occur are of such a magnitude that the electron energies are of the order of a fraction of an electron volt, and at these low energies the problems associated with experimental determinations of the cross-sections become complex. Consequently there is a deficiency of experimental data. It is therefore essential to have theoretical methods for calculating the cross-sections.
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