Magnetic susceptibility of Cs and Rb from the vapor to the liquid phase

We apply the model of a partially ionized gas to calculate the electronic magnetic susceptibility of Cs and Rb vapor along the coexistence curve. The deviations from the Curie law as obtained in the experiments of Freyland [Phys. Rev. B 20, 5104 (1979) and J. Phys. (Paris) Colloq. 41, C8-74 (1980)] are due to the formation of spin paired dimers. The enhancement of the electronic magnetic susceptibility at about 2–3 times the critical density in the domain of the expanded liquid can be explained by the formation of higher clusters such as ${\mathrm{Cs}}_2^{+}$ and ${\mathrm{Rb}}_2^{+}$. The implications on the mechanism of the metal-nonmetal transition in expanded liquid metals are discussed.