Electron-photon angular correlation measurements of He (1S01−2P11) excitation by electron impact at 80 eV

The electron-photon angular correlation function was measured between 80-eV electrons which excited the $2{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of helium and 58.4-nm photons from the decay of that state for electron scattering angles ranging from 5° to 100°. The data have been analyzed to yield values of the ratio $\lambda$ of the differential cross section for exciting the $M_j=0\mathrm{}$ sublevel to the total differential cross section and the magnitude $\left|\chi \right|$ of the phase difference between the $M_j=0\mathrm{}$ and $M_j=1\mathrm{}$ excitation amplitudes. The data agree with all previous measurements within one standard deviation, with the exception of the large-angle values of $\lambda$ obtained by Hollywood, Crowe, and Williams. Possible causes of these discrepancies are discussed. The values of $\lambda$ and $\left|\chi \right|$ obtained in this work agree quite well with those given by the distorted-wave calculations of Madison over the entire angular range.