A method of calculation of the thermodynamic properties of Ar3

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.