Simultaneous Ionization and Excitation of Neon by Electron Impact

Abstract

The simultaneous ionization and excitation cross sections by electron impact for the $3p$, $3d$, and $4s$ levels in neon of the $^{3}P$, $^{1}D$, and $^{1}S$ cores have been examined. The excitation functions were quite broad. In all, over 100 optical cross sections have been measured and over 50 excitation functions from threshold to 1000 eV were obtained. The cascade lines from the $3d$ and $4s$ levels of the various cores were very weak, with some at the limit of detectability. The error of these cascade cross sections ranges from 10 to 50%. The direct-excitation cross sections were obtained for the $3p$ levels of the three cores. Polarization effects were examined and only three levels exhibited any polarization; these were less than 10%. There are no previous experimental measurements of these cross sections. The branching ratios obtained by experiment and calculation have been compared with those yielded by our work. These branching ratios, the lack of strong lines between doublet and quartet levels, and the general tendency of the quartet excitation functions to be more peaked than the doublets leads us to accept the $(^{3}P)3p$ levels as being well designated by $\mathrm{LS}$ coupling. In conjunction with this and the exceptionally broad excitation functions, it appears that the ionization cross section influences the energy dependence of the simultaneous ionization and excitation cross section. The high-energy portion of the excitation functions tended to bear this out as well. The sudden-perturbation approximation has been applied to several of the $3p$ levels; its numerical values for the cross sections were two or three times greater than the experimental values. The cross section of most observed levels falls off with electron energy $E$ as ${E}^{\ensuremath{-}1}$. Theory tends to indicate a $\frac{(\mathrm{ln}E)}{E}$ dependence at high energy.