\begin{table}%T5
\caption{New species and alterations to chemical formulae. For the latter, we specify the old 
representation followed by the new.}
  \label{changes}
%\centering
\small
\begin{tabular}{llllllll}
\hline \hline 
\noalign{\smallskip}
%%
\multicolumn{8}{l}{New species}\\
 F      & F$^+$       & HF$^+$     & HF      & H$_2$F$^+$     & CF$^+$   & C$_3$H$_6^+$ & C$_3$H$_7^+$  \\
 NH$_2$CN  & NH$_2$CNH$^+$  & N$_2$O$^+$    & HN$_2$O$^+$   & HCOOH$^+$   & SiF$^+$  & NCCN  & NCCNH$^+$ \\
 H$_3$C$_3$N$^+$ & C$_4$H$_7^+$    & CH$_3$CS$^+$  & C$_4$N     & NCCNCH$_3^+$ & C$_6$H$_6^+$ & C$_{10}$ \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
\multicolumn{8}{l}{Altered chemical formulae}\\
\multicolumn{2}{l}{C$_3$H$_4$ by CH$_3$CCH} & \multicolumn{2}{l}{H$_4$C$_2$N$^+$ by CH$_3$CNH$^+$} & \multicolumn{2}{l}{H$_5$C$_2$O$^+$ by CH$_3$CHOH$^+$} & \multicolumn{2}{l}{C$_2$H$_6$OH$^+$ by CH$_3$OCH$_4$$^+$} \\
 \multicolumn{2}{l}{C$_2$H$_7$O$^+$ by C$_2$H$_5$OH$_2$$^+$} &  \multicolumn{2}{l}{H$_2$C$_3$N$^+$ by HC$_3$NH$^+$} & \multicolumn{2}{l}{H$_3$C$_3$N by CH$_2$CHCN} & \multicolumn{2}{l}{C$_3$H$_6$OH$^+$ by C$_2$H$_6$COH$^+$}\\
\multicolumn{2}{l}{C$_5$H$_4$ by CH$_3$C$_4$H} & \multicolumn{2}{l}{H$_3$C$_4$N$^+$ by CH$_3$C$_3$N$^+$} & \multicolumn{2}{l}{H$_3$C$_4$N by CH$_3$C$_3$N}    & \multicolumn{2}{l}{H$_4$C$_4$N$^+$ by CH$_3$C$_3$NH$^+$} \\
 \multicolumn{2}{l}{C$_7$H$_4$ by CH$_3$C$_6$H}    & \multicolumn{2}{l}{H$_3$C$_6$N by CH$_3$C$_5$N}    & \multicolumn{2}{l}{H$_4$C$_6$N$^+$ by CH$_3$C$_5$NH$^+$} & \multicolumn{2}{l}{H$_3$C$_8$N by CH$_3$C$_7$N} \\
 \multicolumn{2}{l}{H$_4$C$_8$N$^+$ by CH$_3$C$_7$NH$^+$}  \\
\noalign{\smallskip}
\hline
\end{tabular}
\end{table}