\begin{table}%t4
   %\centering
\par
      \caption{Summary of variations of standard model parameters.\label{result-summary}}
        \begin{tabular}{ll}
	 \hline\hline
         \noalign{\smallskip}
         Parameters varied &  Range \\
         \noalign{\smallskip}
         \hline
         \noalign{\smallskip}
         1) C/O ratio  				& 0.21--1.20\\
         2) Metal depletion			& low-metal -- additional depletion of real metals by factors of~2\\
                                                & low-metal -- high-metal\\
         3) Cosmic-ray ionization rate $\zeta$  & $1.3\times10^{-18}$ s$^{-1}$--$1.3\times10^{-16}$ s$^{-1}$\\
         4) Gas-density $n_{\rm H}$		 	& $2\times10^3$ cm$^{-3}$--$2\times10^5$ cm$^{-3}$\\
         5) C$_{3}$H$_{2}$ + H fraction         &  0.50--1.00\\
         \hline
      \end{tabular}
       \end{table}