  The thermal degradation of a graphene-like two-dimensional triangular
membrane with bonds undergoing temperature-induced scission is studied by means
of Molecular Dynamics simulation using Langevin thermostat. We demonstrate that
the probability distribution of breaking bonds is highly peaked at the rim of
the membrane sheet at lower temperature whereas at higher temperature bonds
break at random anywhere in the hexagonal flake. The mean breakage time $\tau$
is found to decrease with the total number of network nodes $N$ by a power law
$\tau \propto N^{-0.5}$ and reveals an Arrhenian dependence on temperature $T$.
Scission times are themselves exponentially distributed. The fragmentation
kinetics of the average number of clusters can be described by first-order
chemical reactions between network nodes $n_i$ of different coordination. The
distribution of fragments sizes evolves with time elapsed from a
$\delta$-function through a bimodal one into a single-peaked again at late
times. Our simulation results are complemented by a set of $1^{st}$-order
kinetic differential equations for $n_i$ which can be solved exactly and
compared to data derived from the computer experiment, providing deeper insight
into the thermolysis mechanism.
