\begin{table}
\begin{center}
\begin{tabular}{lll}
\hline\\
$A_{H^+}         $ & 
    $8.4 \times 10^{-11} T^{-1/2} T_3^{-0.2} (1 + T_6^{0.7})^{-1}$ & 
    RR for H$^{+}$ 
\\[.5em]
$A_{d}           $ &
    $1.5 \times 10^{-10} T^{-0.6353}$    & 
    dielectronic RR for He$^{+}$ 
\\[.5em]
$A_{He^+}        $ & 
    $1.9 \times 10^{-3} T^{-1.5} \mathrm{e}^{-470000/T} (1 + 0.3 \mathrm{e}^{-94000/T})$    & 
    RR for He$^{+}$
\\[.5em]
$A_{He^{++}}     $ & 
    $3.36 \times 10^{-10} T^{-1/2} T_3^{-0.2} (1 + T_6^{0.7})^{-1}$    & 
    RR for He$^{++}$
\\[.5em]
\hline\\
$\Gamma_{H^{0}}  $ & 
    $5.85 \times 10^{-11} T^{1/2} \mathrm{e}^{-157809.1/T} ( 1 + T_5^{1/2})^{-1}$& 
    CIR for H$^{0}$
\\[.5em]
$\Gamma_{He^{0}} $ & 
    $2.38 \times 10^{-11} T^{1/2} \mathrm{e}^{-285335.4.1/T} ( 1 + T_5^{1/2})^{-1}$& 
    CIR for He$^{0}$
\\[.5em]
$\Gamma_{He^{+}} $ & 
    $5.68 \times 10^{-12} T^{1/2} \mathrm{e}^{-631515/T} ( 1 + T_5^{1/2})^{-1}$& 
    CIR for He$^{+}$
\\[.5em]
\hline
\end{tabular}
\end{center}
\caption{Temperature ($T$) dependent recombination rates (RR) and collisional ionization rates 
(CIR) for Hydrogen and Helium species, adapted from \citet{katzCosmologicalSimulationsTreeSPH1996}. 
All rates are in units of cm$^3$ s$^{-1}$. $T_n$ is shorthand for $T / 10^n$K.}
\label{tab:coll-ion-rates-katz}
\end{table}