\begin{table}%t5
\caption {\label{tab:c2h21p}Observed hyperfine structure components of the $N'\rightarrow N=2\rightarrow1$ transition 
  in \cch: rest frequencies$^a$, residuals $\rm o-c$ between observed and calculated frequencies$^b$, 
  and relative intensities~$f$.} % title of Table 
%\centerline
 {\begin{tabular}{c c c r c} 
\hline\hline % inserts double horizontal lines 
Comp. & Transition & $\nu$ & $\rm o-c$ & $f$ \\ % table heading
no. &$J',F'\rightarrow J,F$ & [MHz] & [kHz] & \\  
\hline % inserts single horizontal line 
1 & $5/2,2\rightarrow3/2,2$ & 174634.861~(16) &     6 & 0.017\\
2 & $5/2,3\rightarrow3/2,2$ & 174663.199~(12) &     0 & 0.350\\
3 & $5/2,2\rightarrow3/2,1$ & 174667.629~(14) & $-$12 & 0.232\\
4 & $3/2,2\rightarrow1/2,1$ & 174721.744~(14) &  $-$8 & 0.197\\
5 & $3/2,1\rightarrow1/2,0$ & 174728.071~(12) &    12 & 0.083\\
6 & $3/2,1\rightarrow1/2,1$ & 174733.210~(14) & $-$15 & 0.052\\
7 & $3/2,2\rightarrow3/2,2$ & 174806.843~(14) &  $-$7 & 0.045\\
\hline 
\end{tabular}}
\par
\smallskip
$^a$ Numbers in parentheses are one standard deviation in units of the least significant figures.\\ 
$^b$ Calculated from present set of spectroscopic parameters in Table~\ref{CCH_parameters}.
\end{table}