Effects of the mean free path and relaxation in a model for the aggregationof particles in superfluid media

摘要

In this paper, we study a two-dimensional model for the growth of molecular clusters in superfluidhelium at low temperature. In the model, particles of diameter a follow random ballistic moves oflength 8=a-256a. Upon attachment on the cluster surface, particles allow one-step relaxation to thenearest twofold coordinated site. Average coordination numbers of particles show that in thepresence of relaxation the screening for incoming particles modifies the microscopic structure of thecluster. These results are in qualitative agreement with experimental aggregation of methane in Hedroplets, in which large abundance of fully coordinated sites is observed. The average coordinationnumber increases with 8, showing that screening is relevant when relaxation is present. As thecluster size increases, the corresponding structure clusters changes from a compact to a fractal,typical of ballistic and diffusion limited models, respectively. A scaling ansatz describing thecrossover between the two regimes is proposed.