\begin{table}%T1
     \caption{\label{tab:thres}Energy threshold of reactions induced by positrons. }
   $$ \begin{array}[b]{lc}
\hline
\hline
\mbox{Process}  & \mbox{Threshold (eV)} \\
\hline
\mbox{e$^{+}$ + H $\rightarrow$ Ps + H$^{+}$} & \mbox{6.8} \\
\mbox{e$^{+}$ + H $\rightarrow$ e$^{+}$ + e$^{-}$ + H$^{+}$} & \mbox{13.6} \\
\mbox{e$^{+}$ + H $\rightarrow$ e$^{+}$ + H$^{*}$} & \mbox{10.2} \\
\mbox{e$^{+}$ + H $\rightarrow$ e$^{+}$ + H$^{**}$} & \mbox{12.1} \\
\mbox{e$^{+}$ + He $\rightarrow$ Ps + He$^{+}$} & \mbox{17.8} \\
\mbox{e$^{+}$ + He $\rightarrow$ e$^{+}$ + e$^{-}$ + He$^{+}$} & \mbox{24.6} \\
\mbox{e$^{+}$ + He $\rightarrow$ e$^{+}$ + He$^{*}$} & \mbox{21.2} \\
\mbox{e$^{+}$ + H$_{2}$ $\rightarrow$ Ps + H$_{2}^{+}$} & \mbox{8.6} \\
\mbox{e$^{+}$ + H$_{2}$ $\rightarrow$ e$^{+}$ + e$^{-}$ + H$_{2}^{+}$} & \mbox{15.4} \\
\mbox{e$^{+}$ + H$_{2}$ $\rightarrow$ e$^{+}$ + H$_{2}^{*}$} & \mbox{12.0} 
\\
  \hline
\end{array}$$
\end{table}