THE ANGULAR DISTRIBUTION OF ELECTRONS ELASTICALLY SCATTERED BY HELIUM ATOMS AND BY HYDROGEN MOLECULES,
QUEEN'S UNIV BELFAST (NORTHERN IRELAND) DEPT OF APPLIED MATHEMATICS
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The differential cross sections for the elastic scattering of electrons by helium atoms and by hydrogen molecules were calculated over a wide range of electron impact energies with allowance made for the contribution to the scattering from the static fields of the target systems, for the effect of electron exchange and, in the case of helium, for the polarization of the target atom by the Coulomb field of the incident electron. The approximate methods which have been used include the Born approximation, the first-order exchange approximation and, in the case of helium, the numerical solution of the differential equations derived by making a partial wave analysis and employing the static field approximation together with a polarization potential term. Use was made of the zeroand first-order phase shifts calculated by Morse and Allis from the exact numerical solutions of the appropriate exchange approximation integro-differential equations for the helium case. It is found that the agreement between theory and experiment is quite satisfactory provided the experimental data for the angular distribution of elastically scattered electrons are normalized separately from the calculated differential cross section curves for each energy of impact, though there remains a tendency for the very small and the large scattering angle data to lie somewhat above that predicted by the theory.