Nucleation of water vapor in microcracks on the surface of β-AgI aerosol particles: 1. The structure of nuclei

The precrystallization stage of nucleation of the condensed phase in wedge-shaped microcracks on the surface of β-AgI crystal at 260 K is studied by the Monte Carlo method. The microcrack field has a strong polarizing effect on the nucleus inducing the electrostatic forces of repulsion of molecules inside the nucleus and their attraction to the surface of microcrack walls. The growth of the nucleus in the microcrack passes through a stage of compaction, which is absent for the nuclei growing on the ideal surface. Microcrack surfaces stimulate, on the one hand, the formation of multilayered structures already at the earlier stage of clusterization and, on the other hand, the decomposition of the nucleus into unbound clusters whose main elements are six-and four-membered cycles. The β-AgI substrate shifts the equilibrium in small clusters from cubic to hexagonal symmetry. The analysis of the formation conditions of the known modifications of crystal and amorphous ice renders improbable the emergence of amorphous forms on the surface at the temperature studied; however, this allows us to consider the crystallization of nuclei to ice XI in the presence of microcracks as the probable event.