V. Baranov

The partition functions and thermodynamic properties of small clusters of rare gas atoms

The partition functions Z(T) for the clusters Arn, Krn, and Xen (n=2, 3, and 4) were calculated with the smoothed density of energy levels ρ(E). The latter was determined in the semiclassical approximation by Monte Carlo integration over the phase space and corrected by the rotational asymptotic for the lowest levels and by the trajectory separation method for the bound states above the dissociation threshold. In the temperature range of 5<T<150 K that is of crucial interest for the cluster formation studies in the supersonic jets, the results have an estimated accuracy of about 5%. The structure of the phase space of tetramer (n=4) clusters and their conformational transition dynamics were studied. The possibility of a link between such transitions and clusters melting is discussed.

A method of calculation of the thermodynamic properties of Ar3

Abstract Calculation of the complete energy spectrum of the quantum system Ar 3 is extremely difficult. The reason is the strong nonlinearity that entangles the modes of internal motion even at the lowest energy levels of the system. One can say that vibrations of the trimer are never small and that its vibrational modes are never normal. For our purposes the exact (pointwise) density of states can be replaced by the smoothed density of states. To decrease the errors, the volume Ω( E ) should be converted into the convolution of two sixfold integrals for energies less than − 1. For energy E >− 1 the conformation can represent a relatively stable trimer or it can eventually turn into a “dimer-monomer at infinity” configuration. To distinguish between these two cases, we studied the evolution of the initial state with time by the three-body trajectories method. The method is applicable to the calculation of thermodynamic properties in the low-temperature region 2 T 〈30 K and to the treatment of chemical equilibrium for trimers of rare gases.

Numerical study of a free jet multinozzle source

Abstract In experiments with molecular beams, negative, positive and neutral clusters are usually generated by an influence on the continuous region of the supersonic flow. Such an influence can disrupt the supersonic mode of the flow. A model of a multinozzle source suggested earlier seems prospective and is the object of mathematical simulation. Flow from several orifices is difficult to investigate, so the flow from several slits of infinite length in suitable configuration was studied. The main result of the calculations is that the close localization of sources does not obscure the supersonic flow, and the disturbances introduced into the flow by arising shock wave structures are weak.