Fine structure of the1s2s2pPo4and1s2p2P4doubly excited states in lithiumlike carbon, nitrogen, and oxygen

The fine structure of the $1s2s2p{}_{}{}^4{}_{}{}^{}P_{}^o{}_{}{}^{}-1s2\mathrm{}{p}^2{}_{}{}^4{}_{}{}^{}P$ multiplet in the doubly excited quartet system of three-electron Civ, Nv, and Ovi has been measured using the method of beam-foil spectroscopy. The fine-structure splittings have been determined to within ∼ 5 ${\mathrm{cm}}^{-1\mathrm{}}$ in both the upper and lower states of each ion, and the absolute transition wavelengths have been measured to within ∼ 0.1 Å (∼ ${10}^{-3\mathrm{}}$ eV). The wavelength results show that existing relativistic and nonrelativistic energy separations calculated for these ${}_{}{}^4{}_{}{}^{}P$ states are inaccurate by ∼ 1% for $Z=6-8\mathrm{}$, and that calculations of the fine-structure splittings are inaccurate by (10-20)% for $1s2s2p{}_{}{}^4{}_{}{}^{}P_{}^o{}_{}{}^{}$ and by ≳ 20% for $1s2p^2{}_{}{}^4{}_{}{}^{}P$. Lifetimes have also been measured for the $J=\frac{5}{2}, \frac{3}{2}, \mathrm{and} \frac{1}{2}$ levels of $1s2p^2{}_{}{}^4{}_{}{}^{}P$. Differential metastability is found to be a characteristic feature of these core-excited fine-structure states in all three ions. Comparison with calculated autoionization and $K$ x-ray transition rates for $Z=7\mathrm{} \mathrm{and} 8$ indicates that the $1s2p^2{}_{}{}^4{}_{}{}^{}P_{\frac{5}{2}}^{}{}_{}{}^{}$ lifetime is determined essentially by its autoionization rate to the doublet continuum through magnetic interactions, whereas the $J=\frac{3}{2} \mathrm{and} \frac{1}{2}$ states decay at a slower rate that is more characteristic of the ${}_{}{}^4{}_{}{}^{}P_{}^o{}_{}{}^{}-{}_{}{}^4{}_{}{}^{}P$ radiative transition rate.