\begin{table}%t1
\caption{Initial gas phase abundances of He, C, O, Si, Fe, and CO.}\label{tab0}
\small%\centerline
{\begin{tabular}{cc}     % 2 columns 
\hline\hline       
 Element/ & Abundance$^a$ \\ 
 molecule & [$n$(X)/$n$(H)]           \\
\hline                    
   He & 0.1 \\
   C  & $7.1\times10^{-9}$ \\
   O  & $1.8\times10^{-4}$ \\
   Si & $8.0\times10^{-9}$ \\
   Fe & $3.0\times10^{-9}$ \\
   CO & $1.5\times10^{-4}$ \\
\hline                  
\end{tabular}}
\smallskip
$^{a}$ From the low metal case for dense cloud chemistry \citep{pra82,her89,gra82}.
\end{table}