\begin{table}%t4
\caption{Calculated  column densities (cm$^{-2}$) in $\zeta$ Persei for undetected species.}\label{und}
%\centering
\par
\begin{tabular}{l|ccc}
\hline  \hline
    Species      & Diffuse Phase   & Dense Phase & Total \\
    \hline
D          & 3.6(15)         & 3.0(14)     & 3.9(15)     \\
Si         & 4.0(13)         & 9.5(12)     & 4.9(13)   \\
H$^+$      & 9.6(16)         & 1.8(12)     & 9.6(16)     \\
D$^+$      & 2.5(11)         & 3.0(06)     & 2.5(11)    \\
H$_2^+$    & 1.4(12)         & 1.3(08)     & 1.4(12)    \\
H$_2$D$^+$ & 6.5(09)         & 1.2(06)     & 6.5(09)     \\
OH$^+$     & 7.6(11)         & 3.1(06)     & 7.6(11)     \\
H$_2$O$^+$ & 5.5(11)         & 2.9(06)     & 5.5(11)     \\
H$_3$O$^+$ & 5.2(11)         & 4.5(06)     & 5.2(11)     \\
\hline
\end{tabular}
\end{table}