FORMATION ENTHALPY OF METALLIC DIMERS

It is demonstrated that there is a relation between the dissociation enthalpies of homonuclear diatomic metallic molecules, D0, the heat of vaporisation of the metals in the condensed phase, Delta Hvap 0, and the surface energy of the pure solid metals, gamma s0. For the majority of metallic elements the three quantities are linearly interrelated. There are three types of exceptions: (i) divalent metals like Zn, Cd, Hg, whose free atomic electronic configuration is one of unusually high stability, (ii) metals like Li, Na, Si, Ge, for which the special value of the number of electrons per diatomic molecule (2 or 8, respectively) stabilises the dimer, and (iii) the 3d metals Ti, V, Cr, Mn, Fe, Co, for which magnetic effects apparently affect the simple interrelations. A table of predicted D0 values is presented.