\begin{table}%t1
\caption{Lifetimes in seconds.}\label{tab:lifetime}
\label{tab:lifetimes}
\small%\centerline
 {
\begin{tabular}{lcccc} 
\hline \hline
 & & \multicolumn{2}{c}{This work} & WK69$^a$ \\
   & & Experimental$^b$    & Theory & \\ 
 \hline\\[-3mm]  %\cline{1-2} \cline{3-5}
a\ls[0]{3}{P} & & 1.28 $\pm$ $0.13$  & 1.44   & 1.07     \\
a\ls[1]{3}{P} & & 1.42 $\pm$ $0.22$ & 1.43   & 1.07     \\  
a\ls[2]{3}{P} & & 1.24 $\pm$ $0.04$  & 1.43   & 1.07     \\ 
\hline
\end{tabular}}
\medskip
$^a$ \citet{WK69}.\\
$^b$ The uncertainty quoted is a one standard deviation of the linear fit to the Stern-Vollmer plot.
\end{table}