\begin{table} %t1
  %\centering
\par
    \caption{Used optical data.}
    \label{taboptconst}
           \begin{tabular}{c|l}
       \hline
       \hline
        Energy intervall [eV] & Reference \\
          \hline
          10~000--51.57 & Lynch \& Hunter (\cite{Lynch96}) \\
          51.57--26.0 & interpolation (see text)        \\
          26.--5 & Moravec et~al. (\cite{Moravec76}) \\
          3.5--1.55 & CRC  (\cite{CRC98}) \\
          1.55--0.0124 & Ordal et~al. (\cite{Ordal88}) \\
          0.0124--0.00124 & extrapolation (see text)  \\ \hline
          \end{tabular}
  \end{table}