  There is accumulating evidence for the presence of complex molecules,
including carbon-bearing and organic molecules, in the interstellar medium.
Much of this evidence comes to us from studies of chemical composition, photo-
and mass-spectroscopy in cometary, meteoritic and asteroid samples, indicating
a need to better understand the surface chemistry of astrophysical objects.
There is also considerable interest in the origins of life-forming and
life-sustaining molecules on Earth. Here, we perform reactive molecular
dynamics simulations to probe the formation of carbon-rich molecules and
clusters on carbonaceous surfaces resembling dust grains and meteoroids. Our
results show that large chains form on graphitic surfaces at low temperatures
(100K - 500K) and smaller fullerene-like molecules form at higher temperatures
(2000K - 3000K). The formation is faster on the surface than in the gas at low
temperatures but slower at high temperatures as surface interactions prevent
small clusters from coagulation. We find that for efficient formation of
molecular complexity, mobility about the surface is important and helps to
build larger carbon chains on the surface than in the gas phase at low
temperatures. Finally, we show that the temperature of the surface strongly
determines what kind of structures forms and that low turbulent environments
are needed for efficient formation.
