Paper detail

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.