Résumé : In this paper two correlations are proposed. The first correlation classifies the forty odd known homonuclear diatomic molecules according to the ratio α = ΔH 0 o (vap. M)/D 0 o(M 2) (heat of vaporization of an atom/dissociation energy of the diatomic molecule). Values of α = 0.5 to 1, 1.2 to 2.5 and >5 correspond to three categories each consisting of several whole groups of elements. The significance of this classification is discussed qualitatively. The second correlation shows that ΔH 0 o(vap. M) can be closely represented by Λ-BΣ iε i(M). Σ iε i(M) is the energy necessary to excite the atoms to a promoted " configuration " composed of equal contributions of a well-defined set of low lying electronic states of the free atom. Λ and B are empirical parameters. One set of electronic states is taken for Ca to Ni, Sr to Pd, and Ba to Pt with B = 1/2 and Λ = 178, 206, 250 kcal/g atom respectively; another set of electronic levels and Λ = 131 kcal and B = 1/4 represent ΔH 0 o(vap. M) for Ni, Cu, Zn, Pd, Ag, Cd, Pt, Au, Hg. Using the first classification, the experimental conditions are estimated for observation of the yet unknown homonuclear diatomic molecules of the transition elements. For this purpose a self-consistent set of free energy functions has been calculated.