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 int eraction potential change during the expansion of the liquid metals fr om the melting point towards their liquid-vapour critical point. Near their critical point, the change from a liquid metal to a non-metal ta kes place, which implies that the interatomic forces must exhibit dras tic changes when the critical point is approached. The static structur e 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 addi tional information about dynamical properties, such as the self-diffus ion coefficient, single particle and collective excitations, measureme nts of the dynamic structure factor of expanded liquid rubidium have b een performed. In particular, these measurements provide information a bout the existence of collective phonon-like excitations in the expand ed liquid metal and about the transition region from collective to mor e localized dynamical behaviour as the metal-non-metal transition is a pproached.