\begin{table}%t5
\caption{Observed ice composition towards Elias 16, expressed as a percentage of H$_2$O abundance $^1$.}
\label{tab5}
%\centerline
{\begin{tabular}{lccc}
\hline
\hline\noalign{\smallskip}
Species  & Elias 16 & \multicolumn{2}{c}{Model M2}  \\
         &          & $2\times10^{5}$ yr & $2.8\times10^{6}$ yr \\
\hline\noalign{\smallskip}
H$_2$O$~^{2,3}$ & 1.28(--4) & 3.47(--5) & 1.50(--4) \\
CO$~^3$ & 26 & 7.4 & 0.3 \\
CO$_2$$~^4$ & 20 & 4(-2) & 0.3 \\
CH$_4$$~^5$ & -- & 20.7 & 28.5 \\
CH$_3$OH$~^5$ & $<$3 & 6.4 & 10.5 \\
H$_2$CO$~^5$ & -- & 5.7 & 1.0 \\
H$_2$O$_2$$~^5$ & $<$$5$ & 3(--4) & 5(--5) \\
OCS $~^5$ &  $<$0.2 & 9(--13) & 6(--14) \\
NH$_3$$~^5$ & $<$$9$ & 12.6 & 7.3 \\
\hline
\end{tabular}}
\medskip
$^{1}$ $a(b) = a \times 10^{b}$; 
$^{2}$ H$_2$O fractional abundance; 
$^{3}$ Ref. \cite{nummelin01a}; 
$^{4}$ Ref. \cite{bergin05a}; 
$^{5}$ data collated by \cite{gibb00a}
\end{table}