\begin{table}%t2
    \caption{\label{initialabundances}Initial abundances at~$t=0$ relative to H$_{2}$ for AFGL~2591.}
    %\centerline
{
                  \begin{tabular}{lll}
            \hline\hline
            Species & Initial abundance & Ref. \\ 
            \hline
     Initial abundance ($T>100~{\rm K}$) & {} & {} \\
     CO & $3.7(-4)$ & a \\
     CO$_{2}$ & $3.0(-5)$ & d \\
     H$_{2}$O & $1.5(-4)$ & d \\
     H$_{2}$S & $1.6(-6)$ & h \\
     N$_{2}$  & $7.0(-5)$ & e \\
     CH$_{4}$ & $1.0(-7)$ & e \\
     C$_{2}$H$_{4}$ & $8.0(-8)$ & e \\
     C$_{2}$H$_{6}$ & $1.0(-8)$ & e \\
     O & $0.0(0)$ & e \\ 
     H$_{2}$CO & $1.2(-7)$ & e \\
     CH$_{3}$OH & $1.0(-6)$ & e \\
     S  & $0.0(0)$ & e \\
     Fe & $2.0(-8)$ & e \\
    % {} & {} & {} \\
     Initial abundance ($T<100~{\rm K}$) & {} & {} \\
     CO & $3.7(-4)$ & a \\
     CO$_{2}$ & $0.0(0)$ & f \\
     H$_{2}$O & $0.0(0)$ & f \\
     H$_{2}$S & $0.0(0)$ & f \\
     N$_{2}$  & $7.0(-5)$ & e \\
     CH$_{4}$ & $1.0(-7)$ & e \\
     C$_{2}$H$_{4}$ & $8.0(-8)$ & e \\
     C$_{2}$H$_{6}$ & $1.0(-8)$ & e \\
     O & $8.0(-5)$  & g \\
     H$_{2}$CO & $0.0(0)$ & f \\
     CH$_{3}$OH & $0.0(0)$ & f \\
     S  & $6.0(-9)$  & h \\ 
     Fe & $2.0(-8)$ & e \\
            \hline
     \end{tabular}}
     \smallskip
$^{{\rm  }}$ $a(b)$ means $a \times 10^{b}$.\\ 
$^{{\rm  }}$ All abundances are gas-phase, and relative to H$_{2}$. \\
$^{{\rm a}}$ van~der~Tak et~al. (\cite{vdt1999}); 
$^{{\rm b}}$ van~der~Tak et~al. (\cite{vdt2000}); 
$^{{\rm c}}$ van~der~Tak \& van~Dishoeck (\cite{vv2000}); 
$^{{\rm d}}$ Boonman et~al. (\cite{boonmanetal2000}); 
$^{{\rm e}}$ Charnley (\cite{C97}); 
$^{{\rm f}}$ assumed frozen-out or absent in cold gas-phase, 
$^{{\rm g}}$ taken to be $\sim$ consistent with Meyer et~al. (1998);
$^{{\rm h}}$ Doty et~al. (\cite{dotyetal2002}).
   \end{table}