Nucleation and stabilization of carbon-rich structures in interstellar
  media
  We study conditions under which carbon clusters of different sizes form and
stabilize. {We describe an approach to equilibrium by simulating tenuous carbon
gas dynamics to long times.} First, we use reactive molecular dynamics
simulations to describe the nucleation of long chains, large clusters, and
complex cage structures in carbon and hydrogen rich interstellar gas phases. We
study how temperature, particle density, presence of hydrogen, and carbon
inflow affect the nucleation of molecular moieties with different
characteristics, in accordance with astrophysical conditions. We extend the
simulations to densities which are orders of magnitude lower than current
laboratory densities, to temperatures relevant to circumstellar environments of
planetary nebulae, and to longtime (microsecond) formation timescales. We
correlate cluster size distributions from dynamical simulations with
thermodynamic equilibrium intuitions, where at low temperatures and gas
densities, entropy plays a significant role.
