\begin{table}%t2
\caption{\label{table_fragmentation}Comparison of the physical parameters for graphite and a-C:H.}
\par
\small%\centerline
 {
\begin{tabular}{l c c c c} 
\hline \hline
 & \multicolumn{2}{c}{Fragmentation} & \multicolumn{2}{c}{Vaporization} \\
Parameter & Graphite & a-C:H & Graphite & a-C:H \\ 
\hline 
$\rho_{0}$ [g cm$^{-3}$] & 2.2 & 1.4 & 2.2 & 1.4\\
$c_{0}$ [km s$^{-1}$] & 1.8 & 1.0 & 1.8 & 1.0 \\
$s$ & 1.9 & 1.9 & 1.9 & 1.9\\
$P_{\rm th}$ [dyne $\rm cm^{-2}$] & $0.4 \times 10^{11}$ & $0.2 \times
10^{11}$ & $5.8 \times 10^{12}$ & $2.8 \times 10^{12}$\\
$\varepsilon_{\rm v}$ [erg $\rm g^{-1}$] & $1.8 \times 10^{9}$ & $0.75
\times 10^{9}$ & $6.4 \times 10^{11}$ & $5.2 \times 10^{11}$ \\
$v_{\rm th}$ [km $\rm s^{-1}$] & 1.2 & 0.8 & 23 & 20 \\
$E_{\rm b}$ [eV] & 0.02 & 0.01 & 8 & 6.5 \\
\hline
\end{tabular}}
\medskip 
Note. Physical parameters for fragmentation and vaporization for a-C:H (this work) and for graphite/amorphous carbon \citep{tielens94}. $c_0$~is the sound speed, $s$~is a dimensionless parameter, $P_{\rm th}$, $\varepsilon_v$ and $v_{\rm th}$  are the relevant threshold pressure, energy density and velocity, respectively. $E_{\rm b}$~is the binding energy.
\end{table}