\begin{table}%T1
\caption{\label{yieldtab}The production rate and yield of H$_2$CO~and the yield of CH$_3$OH.}
\small%\centerline
{
\begin{tabular}{cccccc}
\hline\hline\noalign{\smallskip}
$T$ & Rate(H$_2$CO)$_{t=0}$$^a$  & Yield (H$_2$CO)$^b$ & Yield (CH$_3$OH)$^{b}$ & Steady state &  Calc.~pen.~column$^{c}$\\
(K) & (10$^{-3}$ molec./H~atom) & (10$^{15}$~molec.~cm$^{-2}$) & (10$^{15}$~molec.~cm$^{-2}$) & & (10$^{15}$~molec.~cm$^{-2}$)\\
\hline
12.0 & 9.0 & 1.2 & 0.8 & yes &  2.0\\
13.5 & 7.3 & 1.0 & 1.4 & yes &  2.4\\
15.0 & 3.2 & 0.9 & 1.6 & yes &  2.5\\
16.5 & 1.1 & 0.8 & 0.6 & no \\
18.0 & 1.0 & 0.5 & 0.2 & no \\
20.0 & 0.9 & 0.4 & 0.1 & no\\
\hline
\end{tabular}}
\smallskip
$^{a}$ {Rate at $t=0$ determined from slope.}\\
$^{b}$ {Yield after three hours of H-atom exposure which corresponds to a fluence of $5.4\times 10^{17}$~H~atoms~cm$^{-2}$. The steady state yield is not reached for all temperatures (fifth column).}\\
$^{c}$ {Penetration column obtained from Cols.~3, 4, and~6.}
\end{table}