Low-energy measurements of electron-photon angular correlation in electron-impact excitation of the2P1state of helium

Abstract

Electron-photon angular correlations between electrons which have excited the $2^{1}P$ state of He and photons from the $2^{1}P\ensuremath{\rightarrow}1^{1}S$ transition have been studied for 27-, 30-, 35-, and 40-eV incident electrons. Values of $\ensuremath{\lambda}$ and $|\ensuremath{\chi}|$ obtained from these measurements are compared to values obtained in distorted-wave and $R$-matrix calculations. The values of $\ensuremath{\lambda}$ and $|\ensuremath{\chi}|$ have been combined to examine the behavior of $|{O}_{1\ensuremath{-}}^{\mathrm{col}}|$ [$\ensuremath{\lambda}(1\ensuremath{-}\ensuremath{\lambda})sin|\ensuremath{\chi}|$], the nonvanishing component of orientation. At 27 eV, a substantial decrease was observed in the values of $\ensuremath{\lambda}$ and $|{O}_{1\ensuremath{-}}^{\mathrm{col}}|$, compared with their values for $E>~30$ eV.