\begin{table}%t1
\caption{List of the strongest hydrogen recombination lines studied in this
paper. We present the three~strongest lines for the first three series 
of hydrogen atom between excited states: Balmer ($m\rightarrow 2$), 
Paschen ($m\rightarrow 3$) and Brackett ($m\rightarrow 4$). 
For each transition $m\rightarrow n$, we show its name, the rest
frame wavelength, and the oscillator strength (these values
have been taken from \citealt{1957ApJS....3...37G}). 
For illustration, we also present in the fifth column the 
redshifted frequency observed today if emission
took place at $z=1000$. The last column shows the optical depth in 
the line at that redshift ($z=1000$), as computed using our code.}
\label{tab:dataset}
%\centering
\par
\begin{tabular}{@{}lccccc}
\hline 
\hline
Transition & $m$ & $\lambda_{nm}$ ($\AA$) & $f_{nm}$ & $\nu_0(z=1000)$ (GHz)
& $\tau _{nm}(z=1000)$ \\ 
\hline
\multicolumn{6}{c}{Balmer lines ($n=2$)} \\
\hline
H$\alpha$ &  3 & 6562.8 &      0.6407 & 456.3 &  4.53 $\times$ $10^{-5}$ \\
H$\beta$  &  4 & 4861.3 &      0.1193 & 616.1 &  6.14 $\times$ $10^{-6}$ \\
H$\gamma$ &  5 & 4340.5 &      0.0447 & 690.0 &  2.09 $\times$ $10^{-6}$ \\
\hline
\multicolumn{6}{c}{Paschen lines ($n=3$)} \\
\hline
P$\alpha$ & 4 & 18751.0 &   0.8421 &  159.7 &    1.17 $\times$ $10^{-7}$ \\
P$\beta$  & 5 & 12818.1 &   0.1506 &  233.6 &    1.47 $\times$ $10^{-8}$ \\
P$\gamma$ & 6 & 10938.1 &   0.0558 &  273.8 &    4.75 $\times$ $10^{-9}$ \\
\hline
\multicolumn{6}{c}{Brackett lines ($n=4$)} \\
\hline
B$\alpha$ & 5 & 40512.0 &    1.0377 &   73.9 &   2.57 $\times$ $10^{-8}$ \\
B$\beta$  & 6 & 26252.0 &    0.1793 &  114.1 &   3.42 $\times$ $10^{-9}$ \\
B$\gamma$ & 7 & 21655.0 &    0.0655 &  138.3 &   1.09 $\times$ $10^{-9}$ \\
\hline
\end{tabular}
\end{table}