\begin{table}%t4[!htbp]
\caption{Measured and calculated lifetimes  for some of the 
lower levels in \ion{Fe}{xxiii}. 
SS: calculated with SUPERSTRUCTURE and adjusted energies;
AS: calculated with AUTOSTRUCTURE (\citealt{chidichimo_etal:04});
S99: calculated by \cite{safronova_etal:99} using 
relativistic many-body 
perturbation theory (including only $n=2$ levels).
\label{tab:lifetimes}}
%\begin{center}
{\begin{tabular}{@{}rlccll@{}}
\hline\hline\noalign{\smallskip}
$i$  & Level  & Measured  & SS & AS & S99  \\
\hline\noalign{\smallskip}
3 & 2s 2p  $^3$P$_{1}^{\rm o}$ & 17.5 $\pm$ 1.5$^{{a}}$ (ns) &
19.5 & 21.2& -- \\
%
5 & 2s 2p  $^1$P$_{1}^{\rm o}$ & 51 $\pm$ 5$^{{b}}$ (ps) & 
51.5 & 50.6 & 52.7 \\
8 & 2p$^2$  $^3$P$_{2}^{\rm e}$ & 79 $\pm$ 8$^{{b}}$ (ps) &
 76.8 & 75.2 & 76.2 \\
9 & 2p$^2$  $^1$D$_{2}^{\rm e}$ & 100 $\pm$ 8$^{{b}}$ (ps) &
 102.2 & 104.3 & 108 \\
10 & 2p$^2$  $^1$S$_{0}^{\rm e}$ & 34 $\pm$ 5$^{{b}}$ (ps) &
 32.0 & 31.6 & 32.3 \\
\hline
\end{tabular}}
$^{{a}}$ \cite{hutton_etal:97}.\\
$^{{b}}$ \cite{buchet_etal:84}.
%\end{center}
\par
\end{table}