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Concentration of Dimer for BCl3 and Rare Gas Atoms in the BCl3 Isotope Separation

In the low temperature environment generated by supersonic flow in the process of laser assisted retardation of condensation of isotope separation for BCl3, the molecular isotopes BCl3 and carrier gas RG(RG=He,Ne,Ar,Kr,Xe) could form BCl3:RG dimer via contact collision process, the mechanism and relationship between dimer concentration and absolute temperature of dimer involving BCl3 molecules are of great significance to the regulation and selection of isotope separation parameters. In this work, based on the analytic description on the anharmonic interaction potential function of BCl3:RG, and considered the two-body and three-body collision induced association and dissociation of dimer, the concentration of BCl3:RG dimer is obtained with the absolute temperature in the range of 20~40K. The results show that the two-body collision dominates the formation of dimer in the low temperature region; with the initial molar fraction of BCl3 in the range of 0.01~0.1, the BCl3:RG dimer concentration changes approximately linearly with the initial molar fraction of BCl3, indicating that the initial molar fraction not only determines the theoretical upper limit of the dimer concentration, but also dominates the dimer concentration in the low temperature region. When the temperature of the supersonic flow chamber is about 20K, the concentration of BCl3:Kr dimer is the largest one, and the concentrations of other dimers are also presented. Furthermore, we explain the mechanism of laser assisted retardation of condensation in separation of isotopes using a simple model at the molecular scale by adjusting parameters of dissociation energy and stretching vibration frequency of the dimer.