\begin{table}%t3
      \caption{\label{modeldifferencetable}Differences between best fit model for IRAS~16293-2422
                 and~AFGL~2591.}
         %\centerline
{
         \begin{tabular}{lll}
            \hline\hline
            Parameter & IRAS~16293 & AFGL 2591 \\ 
            \hline
     Initial abundance ($T>100~{\rm K}$) & {} & {} \\
     CO & $1.0(-4)$ & $3.7(-4)$ \\
     H$_{2}$S & $1.0(-8)$  & $1.6(-6)$ \\
     H$_{2}$CO & $8.0(-8)$ & $1.2(-7)$ \\
     CH$_{3}$OH & $1.5(-7)$ & $1.0(-6)$ \\
     {} & {} & {} \\
     Initial abundance ($T<100~{\rm K}$) & {} & {} \\
     CO ($20 < T({\rm K}) < 100$) & $1.0(-4)$ & $3.7(-4)$ \\
     O & $1.0(-4)$ & $8.0(-5)$ \\
     H$_{2}$CO ($60 < T({\rm K}) < 100$) & $8.0(-8)$ & $0.0$ \\
     CH$_{3}$OH ($60 < T({\rm K}) < 100$) & $1.5(-7)$ & $0.0$ \\
    % {} & {} & {} \\
     $T_{{\rm des}}({\rm K})$ [$x(T<T_{{\rm des}}) \sim 0$] 
    %    & {} & {} \\
     CO & $20$ & $100$ \\   
     H$_{2}$CO & $60$ & $100$ \\
     CH$_{3}$OH & $60$ & $100$ \\
    % {} & {} & {} \\
     CR ionziation rate $[\zeta]$ (s$^{-1}$) & $5.0(-16)$ & $5.6(-17)$ \\
            \hline
     \end{tabular}}
     \smallskip
$^{{\rm  }}$  $a(b)$ means $a \times 10^{b}$.\\ 
$^{{\rm  }}$ All abundances are gas-phase, and relative to H$_{2}$. \\
   \end{table}