\begin{table}%t2
\caption{\label{Table2}Thickness and density of the samples, stopping powers and the investigated dose ranges.}
%\centering
\small 
\begin{tabular}{l c c c c}
\hline\hline\noalign{\smallskip}
Sample & Thickness & $\varrho$ & Stopping\tablefootmark{a} & Dose range \\
& ($\mu$m) & (g~cm$^{-3}$)& (eV~$\AA^{-1}$) & (eV/16~u) \\
\hline\noalign{\smallskip}
 CO:SO$_2$ = 5:1 & 0.776 & 0.99\tablefootmark{b} & 7.5 & 1.3--80.7 \\
 CO/SO$_2$ layer & 0.480/0.318 & 0.8\tablefootmark{c}/1.93\tablefootmark{d}
 & 6.2/14.2 & 1.3--39.8 \\
 CO:H$_2$S = 10:1 & 0.662 & 0.83\tablefootmark{b} & 6.6 & 1.3--42.2 \\
 CO:H$_2$S = 1:10 & 0.356 & 1.26\tablefootmark{b} & 10.0 & 1.3--42.1 \\
 CO/H$_2$S layer & 0.325/0.148 & 0.8\tablefootmark{c}/1.31\tablefootmark{b}
& 6.1/10.8 & 1.3--42.2 \\
\hline
\end{tabular}
\tablefoot{\tablefoottext{a}{Stopping power of 200~keV protons calculated by the SRIM software (Ziegler et~al. \cite{ziegler96})};  
 \tablefoottext{b}{this work};   
\tablefoottext{c}{Loeffler et~al. (\cite{loeffler05})};  
\tablefoottext{d}{Rudolph (\cite{rudolph77})}.}
\end{table}