Electron-photon angular correlations from electron impact excitation of atoms

Abstract

Electron-photon angular correlations between the inelastically scattered electrons from the excitation of the 21P state of helium and the photons emitted in the deexcitation process have been measured for an incident electron energy of 80 eV and for electron scattering angles in the range of 8 - 108°. For these measurements a new apparatus has been designed and constructed. Because of the existing discrepancy between the experimental results of Hollywood et al. and Sutcliffe et al. great care has been taken during the construction of the apparatus to ensure that the collected data were free from systematic errors. An analysis of the data yields λ, the ratio of the differential cross sections for exciting the Mj = 0 sublevel to the total differential cross section and the magnitude | x I of the phase difference between the Mj = 0 and Mj = 1 excitation amplitudes. The Fano-Macek orientation and alignment parameters are also derived from the present data. The values of the derived parameters are compared to values which have been obtained in other experiments and theoretical calculations. It is found that none of the known theoretical calculations fully agree with the present data which are in good agreement with the experimental results of Hollywood et al., and Slevin et al. but show a marked discrepancy at large scattering angles (θe > 70°) with the data of Sutcliffe et al. and recent measurements of Steph and Golden. Electron-photon angular correlations for the 4p5(2P3/2) 5s3 P1 and 4p5 (2P1/2) 5s1P1 states of krypton and 5p5 (2P3/2) 6s3P1 state of xenon have also been measured. In this case, unlike helium, LS coupling is not valid and spin-orbit interaction in the target atom effects the phase information x. This effect has been experimentally observed for the first time for an incident electron energy of 60 eV and 36 eV in the case of krypton and 80 eV for xenon at 20° and 30° electron scattering angles.