Thermal fluctuations and nanoscale effects in the nucleation of
  carbonaceous dust grains
  We investigate the role of thermal fluctuations and of the finite number of
monomers in small clusters of carbon atoms on the nucleation rate of
carbonaceous grains. Thermal fluctuations are due to the quantized nature of
the energy exchanges between the clusters, the gas, and the radiation field.
Nanoscale effects modify the spontaneous detachment of monomers due to the
finite amount of internal energy contained in small clusters. We find that both
corrections have a big impact on the stability of the clusters and on the rate
of nucleation. We implement our model within a Monte Carlo code to derive the
new stability conditions for clusters as well as nucleation rates. Due to
computing limitations, we can explore the consequences of this approach only at
high temperatures, at which particle interactions are not much less frequent
than photon interactions. We found that the combined effect of the detachment
correction and the temperature fluctuations produces faster nucleation. We also
found that the nucleation rate depends on the composition of the gas and not
only on the partial pressure of the compound that condensates into grains. This
is a unique result of this model that can be used to prove or disprove it.
