Enhancement of excited-state population of magnesium ions upon decay of autoionizing resonances

Decay of autoionizing resonances in atoms often leads to preferential production of excited states of the resulting ion. The population of these states can exceed the population of the ground state by more than an order of magnitude. We report measurements of the branching ratios for ${\mathrm{Mg}}^{+}$ ions resulting from the decay of selected autoionizing levels. These derive either from single excitation of a 2p electron or from two-electron excitations. For excited states of the type 2${\mathit{p}}^5$ ${(}^2$ ${\mathit{P}}_{1/2,3/2}$)3${\mathit{s}}^2$ns, n=4 or 5, production of ${\mathrm{Mg}}^{+}$ ions having the final configuration 2${\mathit{p}}^6$ns is the predominant decay feature. For n>5, the predominant decay feature is the 2${\mathit{p}}^6$(n+1)s configuration, indicating that shakeup is very strong in the decay of the excited state. For excited states of the type 2${\mathit{p}}^5$ ${(}^2$ ${\mathit{P}}_{1/2}$)5d and 2${\mathit{p}}^5$ ${(}^2$ ${\mathit{P}}_{3/2}$)6d, the decay behaves in a manner similar to that of the ns states. However, for the 2${\mathit{p}}^5$ ${(}^2$ ${\mathit{P}}_{1/2}$)6d state, the most prominent decay channel appears to be the 2${\mathit{p}}^6$11d state, which leads to the emission of an electron with the same kinetic energy as the ${\mathit{L}}_2$-${\mathit{M}}_1$ ${\mathit{M}}_1$ Auger line.