Metal‐Nonmetal Transition and Homogeneous Nucleation of Mercury Vapour

The paper presents ionization potentials of mercury clusters obtained by photoelectron spectroscopy which provide evidence that a size‐dependent gradual transition from van der Waals‐type to metallic interaction occurs in Hg x ‐clusters for × > 13. In order to probe the role of this nonmetal to metal transition in the homogeneous nucleation process of supersaturated mercury vapour we have determined the supersaturation necessary for homogeneous condensation of mercury vapour in the temperature range 250 to 320 K. The measurements were made using an upward thermal diffusion cloud chamber. The results demonstrate that none of the current theories for homogeneous nucleation satisfactorily predict the observed critical supersaturations. The measured values are about 3 orders of magnitude lower than the values predicted by the conventional Becker‐Döring‐Zeldovitch‐theory.