\begin{table}%t2
%\centering
\par
\caption{Diamond and nanodiamond size diagnostics based upon the C--H
  stretching vibrations in the~3.4 to 3.7~$\mu$m spectral region.
 \label{tab2} }
\begin{tabular}{cl}  
 \hline
 \hline
 Size range & Characteristic spectral features              \\[0.2cm]
 \hline
  $>$50~nm & Broad bands at 3.4 and 3.5~$\mu$m with        \\
            & well-defined sub-structure bands at           \\
            & 3.41, 3.43, 3.45, 3.50, 3.51 and 3.53~$\mu$m. \\
            & The 3.53~$\mu$m band is particularly strong.  \\[0.2cm]
\par
  50--25~nm & Broad bands at 3.4 and 3.5~$\mu$m with        \\
            & weak sub-structure bands at 3.41, 3.43,       \\
            & 3.45, 3.50, 3.51 and 3.53~$\mu$m. Note that   \\
            & the 3.53~$\mu$m band now only appears as      \\
            & sub-structure.                                \\[0.2cm]
\par
  25--5~nm  & Broad bands at 3.4 and 3.5~$\mu$m with a      \\
            & slight asymmetry due to very weak             \\
            & sub-bands in the red wings. There is          \\
            & a clear dip between the two bands.            \\[0.2cm]
\par
  $<$5~nm  & Broad bands at 3.4 and 3.5~$\mu$m with a      \\
            & hint of very weak sub-bands in the red        \\
            & wings. There is a  less-pronounced dip        \\
            & between the two bands.                        \\[0.2cm]
 \hline
\end{tabular}
\end{table}