\begin{table}%t6
  \caption {\label{table:models}Quantitative description of the chemical composition
    models with the relative percentage of each component. }                  
%\centering
\par
\begin{tabular}{l  l l l  l l  l  l} 
\hline\hline       
\noalign{\smallskip}
Components                    &Model 1       &Model 2       &Model 3      &Model 4    &Model 5    &Model 6  & Reference\\
\hline                                                                                
Amorphous H$_2$O         &13\% (500)    &5\% (600)    &7\%  (400)   &9\% (370)   &5\% (300)  &1\% (200)   &\cite{Grundy+98}\\
Crystalline H$_2$O       &13\% (40)     &3\% (100)    &13\% (160)   &12\% (150)  &3\% (50)   &19\% (200)  &\cite{Grundy+98}\\
Pure NH$_3$              &--            &--           &2\% (120)    &--          &--         &--          &\cite{Schmitt+98}\\
NH$_3$:H$_2$O (1:99)      &--            &13\% (150)   &--           &--          &11\% (300) &--          &T. Roush (Priv. comm)\\
Pure CH$_4$              &--            &6\% (800)    &5\% (800)    &5\% (800)   &--         &--          &\cite{Quirico+97}\\
Amorphous C              &71\% (10)     &71\% (10)    &71\% (10)    &71\% (10)   &71\% (10)  &58\% (10)   &\cite{Zubko+96}\\
Titan tholin             &3\% (10)      &2\% (10)     &2\% (10)     &3\% (10)    &0\% (10)   &1\% (10)    &\cite{Khare+84}\\
C$_2$H$_6$               &--            &--           &--           &0\% (20)    &--         &7\% (600)   &\cite{Quirico+97}\\
NH$_4^+$                 &--            &--           &--            &--          &9\% (800)  &13\% (800)  &J. Cook (Priv. comm.)\\
Reduced $\chi^2$         &1.78          &\textbf{1.29}&\textbf{1.32}&1.35 &1.64       &\textbf{1.23}    &\\
\hline                  
\end{tabular}
\tablefoot{Grain
    size in micron is indicated in parenthesis. Models are sorted on
    Fig.~\ref{fig:models} from bottom (model~1) to top (model~6).}
\end{table}