Ionization of the He, Ne, Ar, Kr, and Xe isoelectronic series by proton impact

Abstract

In this paper we report ionization cross sections of positive ${\mathrm{Li}}^{+}$, ${\mathrm{Na}}^{+}$, ${\mathrm{K}}^{+}$, ${\mathrm{Rb}}^{+}$, neutral He, Ne, Ar, Kr, Xe, and negative ${\mathrm{F}}^{\ensuremath{-}}$, ${\mathrm{Cl}}^{\ensuremath{-}}$, ${\mathrm{Br}}^{\ensuremath{-}}$, ${\mathrm{I}}^{\ensuremath{-}}$ ions by impact of protons with energies ranging from $25\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1000\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. Cross sections of singly charged ions are relevant to the calculation of electron yields in collisions with insulator surfaces. Calculations were performed within the continuum distorted wave--eikonal initial state method using an angular expansion in spherical harmonics and a numerical evaluation of the radial functions corresponding to both the initial (bound) and the final (continuum) states. The first Born approximation was used on an equal footing. We find that this first-order theory holds for proton energies larger than $300\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. For comparison, we also calculate the shellwise local plasma approximation. Our results show that it gives a good account of the cross sections for neutral targets.