Autoionization of high-lBa 6p1/2nl states

The autoionization rates and energies of the Ba 6$p_{1/2}$nl states for n=11–13 have been measured using a multistep laser-excitation technique. The excitation is via the bound 6snl states which are populated using an electric-field switching method that allows the selective population of the high-angular-momentum states. The results of the measurements indicate an $n^{\mathrm{-}3}$ dependence and a rapid decrease of the autoionization rates with l. For the lowest-l states studied here, l=4, the rates are ≃${10}^{11}$ ${\mathrm{s}}^{\mathrm{-}1}$. At l≃8 the autoionization rates fall below the radiative decay rate of 2×${10}^8$ ${\mathrm{s}}^{\mathrm{-}1}$. Autoionization rates larger than ${10}^{10}$ ${\mathrm{s}}^{\mathrm{-}1}$ are obtained by direct measurements of spectral widths, while smaller rates are determined by a saturation-broadening technique. The autoionization rates are in agreement with calculations based on an nl electron in a hydrogenic orbit around a ${\mathrm{Ba}}^{+}$ core.