Double and single electron capture in slow collisions ofAr9+,8+ ions with He atoms

The technique of 0° Auger-electron spectroscopy has been used to study Na-like ${\mathrm{Ar}}^{7+}$ excited states populated in double- and single-capture collisions by 90-keV ${\mathrm{Ar}}^{9+}$ and 80-keV ${\mathrm{Ar}}^{8+}$ projectiles from He target atoms. Metastable Ne-like ${\mathrm{Ar}}^{8+}$ 2$p^5$3s ${}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}$,2 states play an important role in populating several ${\mathrm{Ar}}^{7+}$ final states. Careful He-target pressure dependence studies were performed to establish the excitation and/or capture mechanism for the Na-like core-excited levels. Highly nonequivalent 2$p^5$3lnl’ configurations, with n values peaking at n=8 but extending to near the series limits, were produced in double-electron capture onto ${\mathrm{Ar}}^{9+}$ projectiles. The spectra have been identified and compared with calculated multiconfiguration Dirac-Fock (MCDF) Auger energies and previous measurements. The Auger decay of the ${\mathrm{Ar}}^{7+}$ 2$p^5$3s3p ${}_{}{}^4{}_{}{}^{}\mathrm{D}_{7/2\mathrm{}}^{}{}_{}{}^{}$ metastable level has been observed and the energy of the line from the Breit induced decay has been measured. Allowed doublet lines from the 2$p^5$3$s^2$ ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{1/2}^{}{}_{}{}^{}$,3/2 states were also measured. The experimental values are in strong agreement with the results of the MCDF calculations.