\begin{table}%t1
\caption{\label{tab:A}Infrared absorption coefficients (band strengths) used in the column density calculations for the observed molecules.} 
%\centerline
 {
 \small \begin{tabular}{ l l l l r }
\hline \hline
Frequency  & Wavelength & Assignment  & Band strength (A) & Ref. \\
(cm$^{-1}$) & ($\mu$m)  & &   (cm molec$^{-1}$) &      \\
\hline\noalign{\smallskip}
2342 & 4.27  & CO$_2^a$ ($\nu_3$)   & $7.6 \times 10^{-17}$   & [1]  \\
$\sim$2234  & 4.48 & N$_2$O ($\nu_3$) & $5.2 \times 10^{-17}$   & [2]  \\
$\sim$2165  & 4.62 & OCN$^-$ ($\nu_3$) & $4 \times 10^{-17}$     & [3]  \\
2139         & 4.67 & CO ($\nu_1$) & $1.1 \times 10^{-17}$   & [4]  \\
$\sim$1100  & 9.09 & NH$_3$ ($\nu_2$) & $1.2 \times 10^{-17}$   & [5]  \\
$\sim$800   & 12.5 & H$_2$O ($\nu_L$)  & $2.8 \times 10^{-17}$   & [4]  \\
\hline 
\end{tabular}}
\medskip 
$^a$ CO$^{18}$O and C$^{18}$O$_2$ at 2325 and 2309~cm$^{-1}$, respectively.
[1]~Gerakines et~al. (\cite{Gerakines1995}); [2] Wang et~al. (\cite{Wang2001}); [3]~d'Hendecourt \& Allamandola (\cite{dHendecourt1986}); [4] Gibb et~al. (\cite{Gibb2004}); [5] Kerkhof et~al. (\cite{Kerkhof1999}).
\end{table}