\begin{table}%T1
\caption{\label{tab1}IR and Raman features of the molecules studied here.}
%\centerline
{
\begin {tabular} {lcc ccc}
\hline \hline
 Molecule & Vibrational mode & \multicolumn {2}{c}{Position (cm$^{-1}$)} & IR & Raman  \\
 & & IR & Raman & & \\
\hline  
H$_2$O & OH sym \& asym stretch & 3300 &3400$^*$ & active & active  \\
H$_2$O & OH bend & 1660 & 1640$^*$ & active & active \\
H$_2$O & libration & 675  & 800 & active & active  \\
CH$_4$ & C-H stretch (asym) & 3010 & 3011 & active & active \\
CH$_4$ & C-H stretch (sym)&  & 2900  & inactive & active  \\
CH$_4$ & C-H deform (sym)& 1534 &1547 & inactive & active   \\
CH$_4$ & C-H deformation & 1300 & & active & inactive \\
CH$_3$OH & O-H stretch & 3260 &3360$^*$  & active & active  \\
CH$_3$OH & C-H stretch (asym)& 2961 & 2950 & active & active  \\
CH$_3$OH & C-H stretch (sym)& 2830 & 2829  & active & active\\
CH$_3$OH & bend \& def & 1460 & 1470 & active & active\\
CH$_3$OH & bend \& def & 1126  & 1107 & active & active \\
CH$_3$OH & C-O stretch & 1034 & 1021  & active & active\\
CH$_3$OH & torsion & 694 &  & active & inactive \\
N$_2$ & N$\equiv$N strecth & 2328 & 2322 & inactive & active \\
\hline
\end {tabular}}
\smallskip
 $^*$ Liquid phase position.
\end {table}
\par
\begin{table}%t2
\par
\caption{\label{tab2}List of studied icy mixtures.}
%\centering
\par
\begin{tabular}{clcclccc}
\hline \hline
 Number & Sample & Ratio & Thickness & Ion \& energy & Fluence & Total dose & Temperature\\
& & & ($\mu$m)& & (ions~cm$^{-2}$)& (eV/16 amu)& (K)\\
\hline
1 & \met & &3.7 & He$^+$, 30~keV & 1.8~$\times$~10$^{15}$ & 64 &12 \\
& & & & He$^+$, 30~keV & 1.8~$\times$~10$^{15}$ & 130 & 100 \\
& & & & Ar$^{++}$, 60~keV & 1.1~$\times$~10$^{15}$& 1000 & 100 \\
2 & \wat:\met:\nn & 1:6:3 & 5 & He$^+$, 30~keV & 3.2~$\times$~10$^{16}$& 825& 12 \\
& & & & He$^+$, 30~keV & 2.0~$\times$~10$^{15}$ &  & 300 \\
3 & \meoh:\nn & 1:2 & 10 & He$^{+}$, 30~keV & 1.2~$\times$~10$^{16}$ & 164 & 12 \\
4 & \meoh:\nn & 1:2 & 10 & Ar$^{++}$, 60~keV  & 1.8~$\times$~10$^{15}$ & 654 & 12 \\
& & & & Ar$^{+}$, 30~keV  & 7.1~$\times$~10$^{16}$ & 1900 & 12 \\
\hline
\end{tabular}
\end{table}