Partial cross sections for excitation of He(3 1D) states by electron impact.

Abstract

We report absolute measurements of a rank four state multipole for He(3${\mathrm{}}^{1}$D) excitation by electron impact with a polarized first-photon--second-photon coincidence technique. The presented technique permits the extraction of total (scattering angle integrated) partial cross sections ${\mathrm{\ensuremath{\sigma}}}_{\mathit{m}}$ for the excitation of He(3${\mathrm{}}^{1}$${\mathit{D}}_{\mathit{m}}$) magnetic substates (m=0,\ifmmode\pm\else\textpm\fi{}1,\ifmmode\pm\else\textpm\fi{}2). The present results stringently test existing theories and, for example, indicate that most theoretical calculations underestimate the partial cross sections ${\mathrm{\ensuremath{\sigma}}}_{0}$ and ${\mathrm{\ensuremath{\sigma}}}_{1}$ and overestimate the ${\mathrm{\ensuremath{\sigma}}}_{2}$. The recent convergent close-coupling calculations of Fursa and Bray [Phys. Rev. A 52, 1279 (1995)] are in excellent agreement with all our measured data. \textcopyright{} 1996 The American Physical Society.