Statistics of internal excitations of atomic systems

The character of internal excitations is compared for phase transitions and chemical transitions in atomic systems. Although the temperature dependenc es of some physical parameters of atomic systems have resonance-like struct ures with maxima in both cases, the dependences of the partition functions on the number of elementary excitations or the excitation energy differ bec ause of the difference in the numbers of interactions that govern the trans itions. The phase changes of condensed rare gases are considered in the cas e where the external pressure is small and the differences between phases a re predominantly associated with differences in configurations. Important e nergy parameters of rare gases are determined by the attractive part of the pairwise interaction potential between atoms. The statistical analysis sho ws the existence of a "freezing limit" temperature for these systems, below which the liquid state becomes unstable. The kinetics of decay of such uns table states is analyzed in terms of the diffusion of voids. (C) 2001 MAIK "Nauka/Interperiodica".