An effective Hamiltonian approach is employed to evaluate the formation energy or binding energy of molecular clusters at 0 K. A generalized statistical-mechanical method to treat both homomolecular and heteromolecular clusters is then introduced in order to evaluate formation energies at finite temperatures. Computed results of formation energies and nucleation rates are found to be in agreement with measurements. It is shown that, in agreement with observation, there exists a simple propensity rule of a linearity between lnJ (J is the nucleation rate) and the inverse of temperature (1/T) for the molecular clusters of interest.

• Received 12 January 1990

DOI:https://doi.org/10.1103/PhysRevA.42.6151