Effect of Virtual Excitation of the 2s and 2p States on the Elastic Scattering of Electrons by Atomic Hydrogen

Abstract

The elastic scattering of electrons by ground state hydrogen atoms, for electron energies below the first threshold of excitation of the atom (10 2 eV), is investigated numerically making full allowance for exchange and for the virtual excitation of the 2s and 2p states of atomic hydrogen. Singlet and triplet phase shifts are obtained for values of the total orbital angular momentum of L = 0, 1 and 2. The results indicate the existence of very narrow resonances just below the n = 2 excitation threshold for several of the spin and angular momentum states. This work was done by an integral equation method, reported previously by Smith, McEachran and Fraser, which explicitly allows for the damped exponential behaviour of the wave functions in the asymptotic region of the closed scattering channels. The results of the present calculation are in very good agreement, except very close to the n = 2 threshold in the orbital angular momentum state L = 1, with the previously reported results of Burke and Schey who have treated this same problem by a different numerical method.