\begin{table}%ta.1
%\centering
\par
\caption{\label{tab:transitions3}Molecular constants~$^{\alpha}$.}
%\centerline
 {\small\begin{tabular}{lccccc}
\hline \hline\noalign{\smallskip}
Species & Transition & Frequency & $E_{\rm u}$/k & $A_{\rm ul}$ & $n_{\rm crit}~^{\beta}$ \\
& ($J_{K}$) & (GHz) & ($K$) & (s$^{-1}$)  & (\cmmthree) \\
\hline
\hcop \rule{0pt}{4mm}& $1\rarr0$ &89.188526 &4.280 &$3.020\times 10^{-5}$  & $3.0 \times 10^{5}$~$^{\dagger}$\\
\hthirteencop \rule{0pt}{4mm} & $1\rarr0$          & ~~86.754330 & ~~4.160  & ~~2.800$\times 10^{-5}$  & $3.0 \times 10^{5}$~$^{\dagger}$\\
\thirteenco \rule{0pt}{4mm}   & $1\rarr 0$         &  110.210353 & ~~5.288 & $6.389 \times 10^{-8}$ & $6.5 \times 10^2$~$^{\dagger}$ \\
\ceighteeno  & $1\rarr 0$   &  109.782173 &  5.267 & 4.961$\times 10^{-7}$ & --  \\
CS   & $2\rarr 1$ & ~~97.980950 & ~~7.052 & $1.703 \times 10^{-5}$ & $2.0\times~10^5$ \\
\ntwohp \rule{0pt}{4mm} & $1_{1}\rarr 0_{1}$  & ~~93.171880 & ~~4.471 & $3.654 \times 10^{-5}$ & $2 \times 10^{5}$~$^{un}$\\
& $1_{2}\rarr 0_{1}$  & ~~93.173700 & -- & --  & -- \\
& $1_{0}\rarr 0_{1}$  & ~~93.176130 & -- & --  & -- \\
\nhthree \rule{0pt}{4mm}  & $1_{1}\rarr 1^{\prime}_{1^{\prime}}$ & ~~23.694480 & 17.215  &  $1.67\times 10^{-7}$ & $2\times 10^{4}$~$^{sw}$\\
& $2_{2}\rarr 2^{\prime}_{~2^{\prime}}$ & ~~23.722630 & 63.866  &  2.29$\times 10^{-7}$ &\\
      \hline
    \end{tabular}}
\medskip
$^{\alpha}$~Unless otherwise noted, all
 values quoted here are sourced from the NASA Jet Propulsion Lab
(JPL) spectral line database \citep{Pickett1998}; $^{\beta}$~Critical density values marked with a $\dagger$ are calculated from the formula ${n_{\rm crit} = A_{\rm ul}/\gamma_{_{H_2}}}$, where ${\rm \gamma_{_{\rm H_2}}}$ is the ``standard'' collisional rate coefficient for H$_2$, assumed equal to 10$^{10}$~${\rm cm^3.s^{-1}.H_2}$-${\rm molecules^{-1}}$. Other values are referenced as follows: $^{un}$~\citet{Ungerechts1997}, 
$^{sw}$~\cite{Swade1989}.
     \end{table}