\begin{table}%t3 [htbp]
  %%\centering

\par
   \caption{\label{tab:DiocotronElectrosphere}Eigenvalues~$\omega$ for the electrospheric model $\Omega_1$, $\Omega_2$ and $\Omega_3$ for some azimuthal modes~$m$.} 
   \begin{tabular}{ccc}
    \hline \hline
    Model & Mode $m$ & $\omega$ \\
    \hline
    $\Omega_1$ &  3 & 6.669 + 1.8715 ~ i \\
    $\Omega_1$ &  8 & 16.74 + 3.1925 ~ i \\
    $\Omega_1$ & 15 & 30.98 + 1.6313 ~ i \\
    $\Omega_2$ &  3 & 6.761 + 0.9759 ~ i \\
    $\Omega_2$ &  5 & 10.90 + 0.765 ~ i \\
    $\Omega_3$ &  3 & 5.643 + 0.3394 ~ i \\
    \hline
  \end{tabular}
\end{table}