\begin{table}
%%\centering
\par
\caption{AFGL $2591$ predicted column densities (cm$^{-2}$) for different 
X-ray models.}\label{tnb}
%\centerline
{
\begin{tabular}{lllllllllll} \hline\hline
 & Model $2$  & & & Model $3$ & & & Model $4$ & & & Model $6$ \\
Species & $N_{{\rm beam}}$ & $q_{2/0}$ & $q_{2/1}$ & $N_{{\rm beam}}$ &  
$q_{3/0}$ & $q_{3/1}$ & $N_{{\rm beam}}$ & $q_{4/0}$ & $q_{4/1}$ & $N_{{\rm beam}}$ \\ \hline
         H & 3.1E+16 &   1.9 &    0.1  & 1.7E+17 &   10.6 &    0.6  & 1.6E+18 &   96.5  &    5.2 & 1.4E+18 \\
         C & 7.5E+13 &   5.4 & 2.0E--02 & 5.2E+14 &   37.2 &    0.1  & 3.2E+15 &  228.9  &    0.7 & 6.0E+15 \\
         N & 8.3E+15 &   7.0 &    2.0  & 1.0E+17 &   84.9 &   24.8  & 1.7E+17 &  145.4  &   42.4 & 1.7E+17 \\
         O & 3.6E+17 &   8.4 &    7.2  & 2.2E+18 &   50.2 &   43.6  & 2.4E+18 &   55.8  &   48.4 & 2.4E+18 \\
         S & 4.1E+14 &   1.0 &    1.1  & 3.2E+15 &    7.9 &    8.2  & 1.5E+16 &   36.2  &   37.6 & 1.3E+16 \\
        CH & 2.0E+11 &   0.4 &    0.2  & 1.9E+11 &    0.4 &    0.2  & 7.4E+12 &   16.8  &    6.5 & 4.7E+12 \\
        NH & 4.0E+12 &   0.5 &    0.5  & 2.2E+12 &    0.3 &    0.3  & 7.4E+12 &    0.9  &    0.9 & 4.8E+12 \\
    NH$_2$ & 1.6E+13 &   0.9 &    1.1  & 1.2E+13 &    0.7 &    0.8  & 4.0E+13 &    2.2  &    2.7 & 2.4E+13 \\
        OH & 8.8E+14 &   0.4 &    0.4  & 2.0E+14 &    0.1 &    0.1  & 1.4E+15 &    0.7  &    0.6 & 1.2E+15 \\
       HCN & 3.5E+15 &   9.3 &    0.8  & 6.0E+15 &   15.9 &    1.4  & 1.1E+15 &    2.9  &    0.2 & 1.7E+15 \\
        CN & 3.9E+11 &   1.5 & 3.0E--02 & 2.5E+12 &    9.5 &    0.2  & 1.3E+13 &   50.0  &    1.1 & 2.1E+13 \\
       HNC & 8.9E+14 &   6.0 &    7.3  & 1.1E+15 &    7.2 &    8.7  & 2.8E+14 &    1.9  &    2.3 & 2.7E+14 \\
    N$_2$O & 5.1E+12 &   1.7 &    1.7  & 1.9E+13 &    6.3 &    6.1  & 7.5E+13 &   24.8  &   24.2 & 6.7E+13 \\
        NO & 4.4E+15 &   0.6 &    0.6  & 6.8E+14 &    0.1 &    0.1  & 3.4E+15 &    0.5  &    0.5 & 2.7E+15 \\
       HNO & 3.7E+12 &   1.2 &    1.2  & 4.5E+12 &    1.5 &    1.5  & 3.3E+13 &   10.9  &   10.9 & 2.4E+13 \\
        SH & 8.3E+11 &   0.8 &    0.5  & 6.0E+11 &    0.6 &    0.4  & 3.6E+12 &    3.3  &    2.2 & 2.7E+12 \\
    H$_2$S & 7.0E+10 &   0.3 &    0.4  & 1.3E+12 &    5.8 &    6.8  & 3.3E+12 &   14.9  &   17.5 & 3.3E+12 \\
        SO & 5.3E+15 &   6.7 &    6.6  & 2.0E+16 &   25.3 &   24.7  & 9.4E+15 &   12.0  &   11.7 & 1.1E+16 \\
        CS & 4.2E+13 &   1.5 &    0.8  & 3.2E+14 &   11.6 &    6.2  & 1.4E+15 &   51.1  &   27.1 & 1.2E+15 \\
     H$^+$ & 2.2E+11 &  14.1 &   14.1  & 4.4E+12 &  278.9 &  278.2  & 4.7E+13 & 2995.3  & 2988.0 & 3.4E+13 \\
    He$^+$ & 1.1E+11 &   2.1 &    2.1  & 6.8E+11 &   12.5 &   12.5  & 6.4E+12 &  117.7  &  117.7 & 4.6E+12 \\
     C$^+$ & 5.5E+11 &   5.0 &    0.1  & 1.0E+13 &   93.4 &    2.5  & 1.1E+14 &  982.8  &   26.3 & 8.0E+13 \\
     N$^+$ & 1.4E+07 &   2.0 &    2.0  & 7.9E+07 &   11.3 &   11.3  & 7.3E+08 &  103.4  &  103.5 & 5.2E+08 \\
     O$^+$ & 1.7E+07 &   7.0 &    2.2  & 1.6E+08 &   65.8 &   20.8  & 1.5E+09 &  631.7  &  199.2 & 1.1E+09 \\
     S$^+$ & 1.2E+11 &   8.2 & 1.0E--02 & 4.2E+12 &  294.1 &    0.5  & 1.1E+14 & 7454.9  &   13.1 & 7.8E+13 \\
   H$_3^+$ & 1.2E+12 &   2.9 &    2.9  & 6.9E+12 &   17.0 &   17.0  & 6.4E+13 &  158.4  &  158.4 & 4.6E+13 \\
H$_3$O$^+$ & 4.0E+13 &   1.2 &    1.1  & 3.6E+13 &    1.0 &    1.0  & 9.2E+13 &    2.7  &    2.5 & 7.9E+13 \\
    OH$^+$ & 5.3E+07 &   8.9 &    3.5  & 9.8E+08 &  164.2 &   65.2  & 9.8E+09 & 1648.7  &  654.7 & 7.0E+09 \\
    CH$^+$ & 9.0E+04 &  28.3 & 4.0E--04 & 6.3E+06 & 1973.4 & 3.0E--04 & 2.9E+08 & 9.0E+04 &    1.2 & 4.9E+08 \\
    CO$^+$ & 1.4E+07 &   3.1 &    1.1  & 5.9E+07 &   13.0 &    4.4  & 5.0E+08 &  109.3  &   36.7 & 3.7E+08 \\
   HCO$^+$ & 4.5E+13 &  25.8 &    9.9  & 3.4E+14 &  193.0 &   74.0  & 1.4E+15 &  783.3  &  300.5 & 1.2E+15 \\
   HOC$^+$ & 1.9E+07 &   1.4 & 2.0E--02 & 7.9E+07 &    5.5 &    0.1  & 7.8E+08 &   54.5  &    0.9 & 1.4E+09 \\
  HCNH$^+$ & 4.3E+12 &   5.6 &    1.2  & 9.7E+12 &   12.8 &    2.8  & 8.4E+12 &   11.1  &    2.4 & 9.7E+12 \\
N$_2$H$^+$ & 3.7E+11 &   3.8 &    3.8  & 2.2E+12 &   22.7 &   22.7  & 1.8E+13 &  189.9  &  190.1 & 1.3E+13 \\
   HCS$^+$ & 3.7E+10 &   5.1 &    0.4  & 1.0E+12 &  135.1 &   10.9  & 1.0E+13 & 1349.3  &  108.7 & 7.8E+12 \\
    SO$^+$ & 3.5E+11 &   4.4 &    1.4  & 3.1E+12 &   38.9 &   12.6  & 9.2E+12 &  116.4  &   37.8 & 8.6E+12 \\
   HSO$^+$ & 6.4E+12 & 145.2 &  143.2  & 3.4E+13 &  766.1 &  755.6  & 1.9E+13 &  423.9  &  418.1 & 2.2E+13 \\
    SH$^+$ & 3.0E+09 &  38.1 &    2.4  & 2.7E+11 & 3494.5 &  218.6  & 3.9E+12 & 5.0E+04 & 3104.7 & 3.0E+12 \\ \hline
\end{tabular}}
\medskip
The beam averaged column densities $N_{{\rm beam}}$ are calculated for 
a $2$\arcsec~ beam ($\approx $2000~AU). The enhancement factor 
$q_{x/y}$ is defined by $N_{i,{\rm Model}~x}/N_{i,{\rm Model}~y}$. Model $0$ 
is the model without any inner radiation field, model~$1$ has no X-rays but an 
inner FUV field ($G_{{\rm 0,in}} = 10$). Models~$2{-}4$ are X-ray models with 
log($L_{{\rm X}}) = 29$, $30$ and $31$, respectively. Model $6$ is one of 
the best fitted models with an inner FUV field $G_{{\rm 0,in}} = 10$, $L_{{\rm X}} 
= 8 \times 10^{31}$~erg~s$^{-1}$,  $T_{{\rm X}} = 10^8$~K and $N_{{\rm H,in}} 
= 3 \times 10^{22}$~cm$^{-2}$.
\end{table}