Electron-photon angular correlations in the electron impact excitation of H(2p)

Inelastically scattered electrons have been detected in coincidence with Lyman alpha photons in the electron impact excitation of the 2p level of atomic hydrogen. Angular correlations have been measured for incident energies of 40, 54.4 and 100 eV at electron scattering angles theta c of 10, 15 and 20 degrees at 200 eV, theta e =10 degrees . Values of the parameters lambda and Re(a 0 a 1 )/ sigma describing the angular correlations have been obtained. The data have also been compared with calculations in the Born, distorted-wave polarised orbital, unrestricted Glauber, distorted-wave Born, classical-path T-matrix, Coulomb-projected Born and hybrid close-coupling approximations. None of these theories appears entirely satisfactory.