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

Abstract

The fine structure of the $1s2s2p^{4}P^{o}\ensuremath{-}1s2{p}^{2}^{4}P$ 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 \ensuremath{\sim} 5 ${\mathrm{cm}}^{\ensuremath{-}1}$ in both the upper and lower states of each ion, and the absolute transition wavelengths have been measured to within \ensuremath{\sim} 0.1 \AA{} (\ensuremath{\sim} ${10}^{\ensuremath{-}3}$ eV). The wavelength results show that existing relativistic and nonrelativistic energy separations calculated for these $^{4}P$ states are inaccurate by \ensuremath{\sim} 1% for $Z=6\ensuremath{-}8$, and that calculations of the fine-structure splittings are inaccurate by (10-20)% for $1s2s2p^{4}P^{o}$ and by \ensuremath{\gtrsim} 20% for $1s2{p}^{2}^{4}P$. Lifetimes have also been measured for the $J=\frac{5}{2}, \frac{3}{2}, \mathrm{and} \frac{1}{2}$ levels of $1s2{p}^{2}^{4}P$. 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 $Z=7 \mathrm{and} 8$ indicates that the $1s2{p}^{2}^{4}P_{\frac{5}{2}}$ 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 $^{4}P^{o}\ensuremath{-}^{4}P$ radiative transition rate.