Polarization effects in the ionization cross section for collisions of Ne

Abstract

At a collision energy E=0.1 eV we see a large polarization effect ${\mathit{Q}}_{\mathrm{ion}}^{\mathrm{*}{\mathit{M}}_{\mathit{j}}\mathrm{*}=0,1}$/${\mathit{Q}}_{\mathrm{ion}}^{{\mathit{M}}_{\mathit{j}}\mathrm{*}=3}$=2.5, decreasing to 1.4 for E\ensuremath{\ge}1 eV. A two-state basis is used for the autoionization width of the \ensuremath{\pi} and \ensuremath{\sigma} orientations of the (2p${)}^{\mathrm{\ensuremath{-}}1}$ core hole, resulting in a preference for the \ensuremath{\Omega}=0,1 molecular states as seen at 0.1 eV. The energy dependence is due to the decrease of ``locking'' of J to the internuclear axis with increasing angular velocity \ensuremath{\varphi}\ifmmode \dot{}\else \.{}\fi{}, leading to the semiclassical criterion ${\ensuremath{\omega}}_{\mathrm{prec}=4\mathrm{\ensuremath{\varphi}}\mathrm{\ifmmode \dot{}\else \.{}\fi{}}}$ for the transition from a space-fixed to a body-fixed description of J.