Electron-Hydrogen Scattering at Low Energies

The effective range in the singlet electron-hydrogen system has been evaluated as 2.646±{}0.004 atomic units by using the asymptotic amplitude of the 202-parameter H^- wave function of Pekeris. This value of the effective range, together with the value of the electron affinity of H^-, determines the scattering length in the singlet system as 6.167 atomic units. The effective range in the triplet system is calculated to be 1.219 atomic units by a Hartree-Fock approximation. It is shown that the effective-range approximation is very good for all energies at which only elastic scattering is allowed. The photo-ionization of H^- is briefly discussed on the basis of the effective-range theory.