Departure from the law of rectilinear diameters for fluids Rb and Cs with delocalized electrons

Terekhov has recently presented a phenomenological model to describe the liquid-vapour critical point. While Terekhov's model embraces a number of equations of state, including both Van der Waals and Dieterici, it leads to the Law of Rectilinear Diameters (LRD). This restricts the applicability to insulating fluids such as Ne and Ar. For the heavy alkalis, Rb and Cs, with delocalized electrons, there are substantial departures from the LRD, which may be due to long-range polarization interaction between the metallic ions.