Measurements of resonance structure in the differential cross sections for the excitation of the n=2 states of atomic hydrogen by high-resolution electron impact

The differential cross sections for the excitation of the n=2 states of atomic hydrogen by high-energy-resolution electron impact have been measured at scattering angles of 33', 54', 70' and 90' over the energy range 11.5 to 12.2 eV, allowing the Feshbach resonances below the n=3 inelastic threshold to be studied. The lowest six of these resonances have been identified as 1 S, 3 P, 1 D, 1 P, 3 F and 3 S/ 3 D respectively, using the classifications of Callaway. At higher energies, the 3 P, 1 D and 1 S states have been tentatively identified. All measured energies agree well with those of Callaway (1982).