STRUCTURE AND DYNAMICS OF EXPANDED LIQUID ALKALI-METALS

The main objective of the study of expanded liquid alkali metals like Rb and Cs is to find out how the structure, dynamics and effective interaction potential change during the expansion of the liquid metals from the melting point towards their liquid-vapour critical point. Near their critical point, the change from a liquid metal to a non-metal takes place, which implies that the interatomic forces must exhibit drastic changes when the critical point is approached. The static structure factor of expanded liquid alkali metals from the melting point up to their critical point have been measured and characteristic changes of the microscopic structure have been observed. In order to obtain additional information about dynamical properties, such as the self-diffusion coefficient, single particle and collective excitations, measurements of the dynamic structure factor of expanded liquid rubidium have been performed. In particular, these measurements provide information about the existence of collective phonon-like excitations in the expanded liquid metal and about the transition region from collective to more localized dynamical behaviour as the metal-non-metal transition is approached.