Auger-electron and x-ray production in 50- to 2000-keV Ne+Ne collisions

Abstract

The production of vacancies in the inner and outer shells of the target and projectile have been studied in ${\mathrm{Ne}}^{i+}$ + Ne collisions in the incident energy range of 45 keV to 2.2 MeV through the observation of $K$ x rays and Auger electrons. Data are given for incident charge states $i=0, 1, \mathrm{and} 2$. Parameters necessary for the analysis of collision kinematics were extracted from previous data and used to investigate these effects on the observed Auger spectra. The kinematic line broadening in the Ne collisions is shown to obscure the peak structure characteristic of the multiple ionization states. The centroid energies and average energy widths of the Auger groups, together with absolute intensities, are reported as a function of the ${\mathrm{Ne}}^{i+}$ energy and electron emission angle for both target and projectile. After kinematic corrections, it is found that target and projectile Auger-electron emission are isotropic to within \ifmmode\pm\else\textpm\fi{} 10% and that the $K$ vacancy created is equally shared between the target and projectile. The average number ${\overline{n}}_{A}$ of electrons removed from the $L$ shell simultaneous with the $K$ vacancy production is estimated from the centroid Auger-electron energies and compared with previously measured data. It is found that ${\overline{n}}_{A}$ increases with the ${\mathrm{Ne}}^{+}$ energy from \ensuremath{\sim}2.5-3.6 over the energy range studied. Absolute cross sections for x-ray and Auger-electron production are reported with an accuracy of about \ifmmode\pm\else\textpm\fi{}15%, and mean fluorescence yields are determined from these cross-section data. The fluorescence yield increases with incident ${\mathrm{Ne}}^{+}$-ion energy, and is consistent with the observed degree of $L$-shell ionization. Total $K$-vacancy production cross sections agree well with available calculations below 200 keV, but the theoretical results underestimate the cross sections at higher energies. This reflects a breakdown of the two-state approximation made in the calculation. Information regarding the coupling of outer-shell molecular orbitals in the entrance channel is extracted from the comparison of the measured data and previous calculations.