Carbon nanoparticles were synthesized from the supersaturated carbon vapor generated in the course of ArF-laser photolysis of carbon suboxide (C3O2). The process of carbon nanoparticle growth was observed by time-resolved laser-induced incandescence (TR-LII) and final particles were analyzed by transmission electron microscopy (TEM). It was found that the particles grow up to the final size of 4-12 nm within 0.02-1 ms. The rate of particle growth and their final size depend on pressure, carbon atom concentration, and bath gas composition. The comparison between the LII- and TEM-based particle sizes yields the information on the thermal energy accommodation coefficients for He, Ar, CO, and C3O2 molecules on carbon particles. A simple model of carbon vapor condensation is proposed.