\begin{table}%t4
%\centering
\par
\caption{\label{tab:cd}Column densities (in \pscm) of H, H$_2$, D and HD
and the molecular fraction $f$ for model~C, obtained from the rate equations~(RC) and from the moment equations~(MC) for different grain temperatures. Numbers in parentheses refer to powers of ten.}
\small \begin{tabular}{lllllll}
\hline\hline
\noalign{\smallskip}
Model    & $T_{\rm dust}$& H &   \rm {H$_2$} & $f$ & D & HD   \\
\hline\noalign{\smallskip}
RC   &  8&  1.87(21)  & 1.60(14)  &1.7(-7)  & 2.76(16) &2.64(10) \\
MC  &       8      & 1.87(21)  & 1.60(14)& 1.7(-7)  &  2.81(16)& 6.26(9) \\
RC   &  10&  1.77(21)  & 5.30(19) & 5.65(-2) &  1.74(16)& 1.07(16) \\
MC  &     10    &  1.84(21) & 1.62(19)& 1.73(-2) &2.28(16)& 5.25(15) \\
RC   &  12&  6.65(19)  & 9.02(20)& 0.96 & 1.26(16)  & 1.55(16) \\
MC  &    12    &  6.33(19) & 9.04(20)& 0.97&  1.26(16) &  1.55(16)\\
RC   &  14&  6.29(19) & 9.04e(20)& 0.97&1.26(16) &1.55(16)\\
MC  &   14     &  6.29(19) & 9.04(20)&0.97&   1.26(16) &  1.55(16) \\
RC   &  16&  6.95(19) & 9.01(20) &0.96 &  1.25(16)&1.56(16)\\
MC  &   16     & 8.87(19) & 8.91(20) & 0.95 & 1.21(16)&  1.60(16) \\
RC   &  18&  1.76(20)& 8.48(20)  & 0.91 &1.07(16)&1.74(16)\\
MC  &   18    &  3.43(20)&  7.64(20) &  0.82 & 8.91(15& 1.91(16) \\
RC   &  20&  9.60(20)& 4.55(20) & 0.49  &7.58(15) & 2.05(16) \\
MC  &   20     & 1.52(21) & 1.77(20) & 0.19  &1.12(16)& 1.69(16)\\
\hline
\end{tabular}
\end{table}