\begin{table}%t4
\caption{\label{table2}Vdz/CASSCF optimized structural parameters.}
%\centerline
 {\small 
 \begin{tabular}{ccccccc}
\hline \hline
State&$T_0$~(eV) th/exp&R(C$_{1}$-C$_{2}$) & R(C$_{2}$-C$_{3}$)&R(C$_{3}$-C${4}$)&$\theta 1$&$\theta 2$\\
\hline
$^3\Pi_u$ & 0.89/0.93 & 1.27 & 1.33 & 1.27 & 180 & 180 \\
$^3\Pi_g$ & 0.63/0.82 & 1.28 & 1.34 & 1.28 & 180 & 180 \\
$^3\Sigma_g^{-}$ & 0 & 1.32 & 1.30 & 1.32 & 180 & 180 \\
\hline
\end{tabular}}
%\medskip
Distances $R$ in $\AA$, angles in degrees and total energies are with respect to the $\rm{X^3 \Sigma}^-_g$ state. The results presented in the table are from this work except the experimental data, which are from \citet{2000Linnartz} for $\rm{ ^3\Pi}_g$ and \citet{1997Xu} for $\rm{^3\Pi}_u$.
\end{table}