\begin{table}%t2
%\centering
\par
\caption{Fitting formulae for momentum transfer coefficients as function of $v_{\rm rms}$ (in km~s$^{-1}$).}\label{rates_vd}
\begin{tabular}{lll}
\hline\hline
Species $s,s^\prime$ &  $\langle\sigma v\rangle_{ss^\prime}$ & $v_{\rm rms}$ \\
 &  (cm$^3$~s$^{-1}$) & (km~s$^{-1}$) \\
\hline\noalign{\smallskip}
HCO$^+$, H$_2$  & $2.40\times 10^{-9} v_{\rm rms}^{0.6}$  & $0.2\lesssim v_{\rm rms}\lesssim 5$\\
H$_3^+$, H$_2$  & $2.00\times 10^{-9} v_{\rm rms}^{0.15}$ & $1\lesssim v_{\rm rms}\lesssim 10$\\
H$^+$, H$_2$    & $3.89\times 10^{-9} v_{\rm rms}^{-0.02}$ & $1\lesssim v_{\rm rms}\lesssim 10$\\
e, H$_2$      & $3.16\times 10^{-11} v_{\rm rms}^{1.3}$ & $20\lesssim v_{\rm rms}\lesssim 200$\\
%\hline
C$^+$,H    & $1.74\times 10^{-9} v_{\rm rms}^{0.2}$ & $2\lesssim v_{\rm rms}\lesssim 20$\\
H$^+$,H    & $2.13\times 10^{-9} v_{\rm rms}^{0.75}$ & $v_{\rm rms} \gtrsim 1$ (GKS) \\
e, H      & $2.50\times 10^{-10} v_{\rm rms}^{1.2}\exp(-v_{\rm rms}/460)$ & $20\lesssim v_{\rm rms}\lesssim 600$\\
%\hline
H$^+$, He   & $1.48\times 10^{-9} v_{\rm rms}^{-0.02}$ & $0.1\lesssim v_{\rm rms} \lesssim 10$  \\
e, He     & $7.08\times 10^{-11} v_{\rm rms}$ & $20\lesssim v_{\rm rms} \lesssim 500$  \\
\hline
\end{tabular}
\end{table}