Nucleation and particle growth are examined for supercooled QF 6 vapor streams diluted in a carrier gas like H 2 , He, N 2 , Ar, or Xe under conditions commonly met in molecular laser isotope separation. Critical cluster radii r * are determined by the usual Kelvin surface-energy correction for a droplet's curvature, but in addition account is taken of a reduction in the intrinsic heat of vaporization of a small cluster due to a decreased average monomer extrication energy. Critical embryo populations are calculated using a new theory published earlier. The results are believed to be an improvement over earlier Farkas-Becker-Doring-Volmer-Zeldovich relations. Time-dependent equations for combined nucleation and particle growth rates in adiabatically cooled gases are formulated, and explicit approximate solutions are derived. As expected, particle growth rates are found to quickly overtake homogeneous nucleation rates, once growth commences. The theory is applied to supersonically expanded UF 6 /N 2 and SF 6 /N 2 flows, and appears generally in agreement with experiment.