\begin{table}%t8
\caption{\label{table_barrieres}Exothermicities used in the two different chemical models. }
\small%\centering
\par
\begin{tabular}{lll} 
\hline
\hline
\noalign{\smallskip}
Reaction & Exothermicity  & Exothermicity \\
& saa model & theo model \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
${\rm CH_3^+ + HD \Leftrightarrow CH_2D^+ + H_2}$ & 370 K& 670 K\\
${\rm CH_2D^+ + HD \Leftrightarrow CHD^+_2 + H_2}$ & 369 K& 433 K\\
${\rm CHD_2^+ + HD \Leftrightarrow CD_3^+ + H_2}$ & 379 K& 443 K\\
${\rm CH_3^+ + D_2 \Leftrightarrow CHD_2^+ + H_2}$ & 713 K& 1005 K\\
${\rm CH_3^+ + D_2 \Leftrightarrow CH_2D^+ + HD}$ & 319 K& 592 K\\
${\rm CH_2D^+ + D_2 \Leftrightarrow CD_3^+ + H_2}$ & 599 K& 564 K\\
${\rm CH_2D^+ + D_2 \Leftrightarrow CHD_2^+ + HD}$ & 317 K& 354 K\\
${\rm CHD_2^+  + D_2 \Leftrightarrow CD_3^+ + HD}$ & 290 K & 151 K\\ 
\hline 
\end{tabular}
\end{table}