\begin{table}%T4
\par
\caption{\label{perturbation2}Additional important reactions for a perturbation amplitude of
1.0, for model~2 and Composition A. }
%\centerline
{
         \begin{tabular}{l|l|rrr}
   \hline
\hline      
Number & Reaction$^{a}$ & $\alpha $&   $\beta $&   $\gamma $ \\
\hline  
168 & C    +   SO$_2$ $\rightarrow $ CO +     SO & & & \\
173 & CH$_2$ +    O $\rightarrow $ CO  +    H  +     H & 1.20e-10  &
0.00  &    0.00 \\
308 & He$^{+}$ +  H$_2$O $\rightarrow $ OH  +  He  +  H$^{+}$ &
1.32e-09  & $-$0.50 & 0.00 \\
309 & He$^{+}$ + H$_2$O $\rightarrow $ OH$^{+}$ + He + H & 1.32e-09
&  $-$0.50  &    0.00\\
333 & He$^{+}$  +   OCS $\rightarrow $ CS + O$^{+}$ + He & 8.40e-10 &
$-$0.50 & 0.00\\
360 & C$^{+}$ + H$_2$O $\rightarrow $ HOC$^{+}$ +   H & 1.80e-09 &
$-$0.50   &   0.00\\
444 & CH$_{3}^{+}$ + S $\rightarrow $ HCS$^{+}$ + H$_2$ & & & \\
447 & CH$_{3}^{+}$ + SO $\rightarrow $ HOCS$^{+}$ +  H$_2$ & 4.20e-09
& $-$0.50 & 0.00 \\
459 & CH$_4$ + S$^{+}$ $\rightarrow $ H$_3$CS$^{+}$ +  H & 1.40e-10 &
0.00 & 0.00\\
509 & O + HCS$^{+}$ $\rightarrow $ S + HCO$^{+}$ & 5.00e-10 &
0.00 &     0.00\\
510 & O  +  HCS$^{+}$ $\rightarrow $ OCS$^{+}$ +   H & 5.00e-10 &
0.00 &     0.00\\
552 & H$_3$O$^{+}$ + H$_2$CO $\rightarrow $ H$_3$CO$^{+}$ +  H$_2$O &
2.60e-09 & $-$0.50 & 0.00\\
553 & H$_3$O$^{+}$ + CH$_4$O $\rightarrow $ CH$_5$O$^{+}$ +  H$_2$O & & & \\
646 & He$^{+}$ + H$_2$O $\rightarrow $ H$_2$O$^{+}$ + He & 1.32e-09 &
$-$0.50 & 0.00\\
663 & C$^{+}$ + S $\rightarrow $ S$^{+}$ + C & & & \\
\hline
\end{tabular}}
\smallskip
$^{a}$  Only rate coefficients that differ by more than 10
percent from the UMIST value are included.
\end{table}