ELASTIC SCATTERING OF ELECTRONS BY HYDROGEN ATOM.

The total orosH sections of elastic; scattering of electrons by hydrogen atom at the incident onorgios of 13.6 ov, 54.4 ov, 122.4 ov.217.6 ev have l)oen calculated in the Born-Opponheiinor (B.O.) approximation with the neglect of the cor© interaction term and taking into account the distortion of the piano incident wave in tho field of tlio torget atom.INTHODXJCTION Tho cross sections of elastic scattering of electrons by atoms are easily cal culated with tho Bom approximation which, however, is valid only at high incident energies; if we include exchange effect in the above, we get the Bora Oppenheimer formula which loads generally to poor results at low energies for exchange scattering amplitudes.As the derivation of the B.O. formula is not logically perfect, a number of modifications of the B.O. approximation have been proposed (Peenberg 1932, Mittleman 1962, Bell and Moiseiwitsch 1963, Ochkur 1964).Ochkur suggests that as the first order Born approximation has been derived according to the first order perturbation theory, the first order B.O. formula for exchange scattering amplitude should not contain terms which are not within the frame work of the first order approximation.So he retains only the first term in the expansion of the B.O. formula in the powers of = wave number of the incident electron).As a result tho effect of the core potential term is neglected.Kang and Sucher (1906) have justified this omission by proving that in the ex change amplitude for electron-atom collision, the core interaction term vanishes identically when the core (proton) is infinitely heavy.Again in the first Born and B.O. formulae the wave function for tho colliding electron is approximated by the incident plane wave on the supposition that the incident energy is high.At low energies, the distortion of the plane waves should be considered.This is generally done by having recourse to higher order approxi mations.In his investigation of the elastic scattering of electrons by helium and hydrogen atoms, Saohl (1968) has given a formulation for taking into account