\begin{table}%t4 %\centering \par \caption{\label{reactions}Surface reactions in the H, O and CO system.} \small \begin{tabular}{lcll} \hline \hline Reactants & &Products & $E_{\rm a}$(K) \\ \hline H + H &$\rightarrow$& H$_2$ & \\ H + O &$\rightarrow$& OH & \\ H + OH &$\rightarrow$& H$_2$O & \\ H + CO &$\rightarrow$& HCO & Table~\ref{Energies} \\ H + HCO &$\rightarrow$& H$_2$CO & \\ H + H$_2$CO &$\rightarrow$& H$_3$CO & Table~\ref{Energies} \\ H + H$_3$CO &$\rightarrow$& CH$_3$OH & \\ O + O &$\rightarrow$& O$_2$ & \\ O + OH &$\rightarrow$& O$_2$ + H & \\ CO + OH &$\rightarrow$& CO$_2$ + H & 176 \\ OH + H$_2$CO &$\rightarrow$& HCO + H$_2$O & \\ OH + H$_3$CO &$\rightarrow$& H$_2$CO + H$_2$O & \\ \hline \end{tabular} \end{table}