A new method for deriving the size of the critical nucleus and the Zeldovich factor directly from kinetic data is presented. Moreover, in principle, the form of G(n)G(n), the free energy of formation of nuclei consisting of nn molecules, can be inferred. The method involves measuring times of first appearance of nuclei of size nn in the transient regime and applying the Becker-Döring theory. Times of first appearance exhibit the same characteristics as the conventional times associated with N(n,t)N(n,t), the number of nuclei of at least size nn per unit volume that have materialized at time tt. That is, they are well represented by three nucleation parameters, the reduced moment, the time lag, and the steady state nucleation rate. But unlike the conventional steady state rate which is independent of nn, the steady state times of first appearance vary with nn. In order to characterize the three nucleation parameters with precision, however, thousands of independent stochastic events with known nn are required. Such sets of data are readily generated in molecular dynamic simulations but, so far, not in laboratory experiments. Results are illustrated by an analysis of simulations of the spontaneous freezing of large clusters of SeF6SeF6.
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