Production of doubly excited projectile states in collisions of 0.1-MeV/u Ag4+ ions with He, H2, and Ar targets.

Abstract

In this work, we study the formation of doubly excited projectile states near the double-escape threshold in collisions of 0.1-MeV/u ${\mathrm{Ag}}^{4+}$ ions with He, ${\mathrm{H}}_{2}$, and Ar gas targets under single-collision conditions. We detect projectile states in which one electron occupies a high Rydberg state and a second electron occupies a low-lying continuum state. The cross sections for producing these doubly excited projectile states are on the order of ${10}^{\mathrm{\ensuremath{-}}20}$ ${\mathrm{cm}}^{2}$. The production probabilities are measured as a function of the continuum-electron laboratory-frame energy with the detected Rydberg electrons arising from a fixed band of energy levels. The width of the continuum-electron energy distribution measured in coincidence with a Rydberg electron is smaller than the width of the energy distribution measured without the coincidence requirement for ${\mathrm{H}}_{2}$ and Ar targets but not for He targets. The width of the continuum-electron energy distribution measured in coincidence with a Rydberg electron decreases as the fraction of doubly excited states formed by projectile double excitation and ionization decreases and the fraction formed by double-target-electron capture increases.