Formation of Clusters in Dense Alkali Plasmas

Abstract

The composition of dense alkali plasmas is calcula+d accounting for the formation of neutral clusters as well as positively and negatively charged molecular ions. The resulting values for the critical point of the liquid-gas phase transition are in better agreement with experimental data as previous theoretical work. The simultaneous occurence of the metal-nonmetal transition is discussed by means of the elctrical conductivity. IntroductionRecently, accurate experimental results were achieved by JUNGST et al. of neutral and charged clusters in the vicinity of the critical point of Rb, Cs and Hg plasmas or fluids, respectively. This is due to the fact that the liquid-gas phase transition is superposed by an ionization equilibrium in alkali and Hg plasmas which yields the simultaneous occurrence of the metal-nonmetal transition. Therefore, a consistent treatment of the ionization equilibrium will lead to improved results for the composition and the electrophysical properties of alkali plasmas compared with previous theoretical work [4, 5, 81. Similar approaches were given recently for hydrogen [6, 181 and xenon plasma [5, 71 investigating the hypothetical plasma phase transition.It is the special aim of the present paper to extend the quantum statistical approach of REDHER and ROPKE [8] to the equation of state of Cs plasma to all alkali metals and to allow for the formation of not only atoms A0 and dimers A, O, but also of trimers A, O and of molecular ions A,,,*. The consideration of these clusters will continue a recent calculation of the thermodynamic properties of the alkali metals Li-Cs of REDMER et al.[9] by allowing for temperatures T < 3000 K and number densities TZ > lo2' m-3, i.e. for nearly critical conditions. As a special result, the critical points of all alkali metals were calculated. The present values modify those published earlier [lo] and lead to a better agreement with the experimental data. This paper is organized as follows: The next section gives a short review of the quantum statistical approach to the equation of state. Section 3 presents the results for the laws of mass action (LMA) which describe the chemical equilibrium between the reacting species in a dense and low-temperature plasma and the parameters which are necessary for their calculation. Explicit results for the composition, the thermodynamic functions and the critical points of the alkali plasmas are given in section 4. Concluding remarks to the metal-nonmetal transition and the electrical conductivity can be found in section 5. 2*

Expanded Fluid Alkali Metals in the Partially Ionized Plasma Model

“…the ionization equilibrium, A+ + e t A, the formation of dimers, 2A * A z , and of molecular ions, A+ + A + A:, are described by respective mass action laws. Taking into account the interactions between the charged particles (screened Coulomb potential), and especially those between charged and neutral particles (polarization) and between neutrals (van der Waals attraction and hard-core repulsion), good agreement with the measured values (deviations less than 10%) was found for the critical temperatures of N a through Cs [8]. …”

“…Within the model of a partially ionized vapor, the equation of state [8], the electrical conductivity [9], and the magnetic susceptibility [lo] of Cs were calculated along the liquid-vapor coexistence line. Reasonable agreement with the experimental data has been achieved and some of the results are reviewed here.…”

Medium modification of two-particle scattering in nonideal Bose systems

“…For the first one, sodium 23 Na, a free ground state scattering length of ±(92 ± 25)a B (in units of the Bohr radius a B ) is obtained from cross section measurement [11]. Spectroscopic data are in agreement with 64 < a 0 /a B < 152 [12], i.e.…”

“…In this paper we apply thermodynamic Green functions for Bose systems and study the microscopic two-particle scattering problem in medium and the resulting equation of state. We discuss the conclusions for two examples with repulsive interaction, sodium 23 Na and rubidium 87 Rb, which play a major role in the BEC experiments.…”

“…Since the recent observation of Bose-Einstein condensation (BEC) in rubidium 87 Rb [1], lithium 7 Li [2] and sodium 23 Na [3] in atom traps at extremly low temperatures new interest has arisen in the investigations of interacting Bose gases. For a comprehensive overview about the current experimental and theoretical activities see [4].…”