\begin{table}%t3
\caption{Band strengths of molecules used for integration.}
\label{strengths}
%\centering
\par
\begin{tabular}{ccccc}   \hline \hline
Species          & Feature         & Position  &           $A$          & Ref.\\
                 &                 & cm$^{-1}$ &     cm molec$^{-1}$    &     \\  \hline   
H$_2$O           & OH stretch      &    3280                & $2.0\times 10^{-16}$ & $^a$ \\ 
NH$_3$           & umbrella (${\nu}_{2}$) &    1070         & $1.7\times 10^{-17}$ & $^b$\\
CH$_3$OH         & CO stretch (${\nu}_{8}$)    &    1026    & $1.8\times 10^{-17}$ & $^c$ \\  
CO               & CO stretch     &    2139                 & $1.1\times 10^{-17}$ & $^d$ \\
CO$_2$           & CO$_2$ stretch (${\nu}_{3}$) &    2343   & $7.6\times 10^{-17}$ & $^e$ \\
HMT & CN stretch (${\nu}_{21}$) &     1234                  & $2.6\times 10^{-18}$ & $^f$ \\
HMT & CN stretch (${\nu}_{22}$) &    1007                   & $5.0\times 10^{-18}$ & $^f$ \\
carboxylic acid salts & COO$^-$ str. & 1586                 & $6.0\times 10^{-17}$ & $^g$ \\ 
NH$_4^+$ & ${\nu}_4$ & 1463                                 & $4.0\times 10^{-17}$ & $^h$ \\  
amides            & C=O str. & 1680                         & $3.3\times 10^{-17}$ & $^g$ \\ 
esters            & C=O str. & 1742                         & $2.0\times 10^{-17}$ & $^g$ \\
POM               &          & 1098                         & $9.7\times 10^{-18}$ & $^i$ \\  
\hline\\[-3mm]
\multicolumn{5}{l}{$^a$ Hagen et~al. (\cite{Hag81});  
$^b$ Sandford \& Allamandola (\cite{San93});
$^c$ Hudgins et~al. (\cite{Hud93});}\\
\multicolumn{5}{l}{
$^d$ Jiang et~al. (\cite{Jia75});
$^e$ Yamada \& Person (\cite{Yam64}); 
$^f$ Bernstein et~al. (\cite{Ber95});}\\
\multicolumn{5}{l}{
$^g$ Wexler (\cite{Wex67}); 
$^h$ Schutte \& Khanna (\cite{Sch03});
$^i$ Schutte et~al. (\cite{Sch93}), in~cm (C~atom)$^{-1}$.}
\end{tabular}
\end{table}