Lifetimes of the metastable autoionizing (1s2s2p)P524states of lithiumlikeAl10+andSi11+ions: Comparisons with theory over the isoelectronic sequenceZ=8−18

Lifetimes of the lowest, most metastable, autoionizing quartet state ($1s2s2p$) ${}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}$ of the lithiumlike ions ${\mathrm{Al}}^{10+}$ and ${\mathrm{Si}}^{11+}$ have been measured by the electron spectrometric, time-of-flight technique and are found to be 2.9 ± 0.2 and 2.1 ± 0.1 nsec, respectively. These results can be compared to very recent Dirac-Hartree-Fock lifetime calculations of Cheng, Lin, and Johnson which give 2.58 and 1.84 nsec, respectively. Comparison of our experimental results for the sequence $Z=8, 9, 13, 14, 16, 17, \mathrm{and} 18$ with the new theoretical calculations are now possible with the result that the measured lifetimes tend to be systematically larger than those predicted from theory, after proper allowance for an $M2\mathrm{}$ radiation-decay channel is made. Possible reasons for these systematic differences are mentioned.