P A Thiel, T E Madey / The interaction of water with solid surfaces: http://www.physics.rutgers.edu/~wchen/Madey_page/Full_Publications/PDF/madey _SSR_1987_T.pdf
"Finally, the magnitude of the chemical bond which water forms with metal surfaces is typically on the order of 40 to 65 kJ/mol (10 to 15 kcal/mol, or 0.4 to 0.7 ev). The experimental basis for thts number is discussed in detail in section 4.2. The strengths of bonds to other types of well-defined surfaces are less-known; heats of adsorption on oxide powders also range from about 40 to 60 kJ/mol [22], which is addressed in section 7.1. Thus, compared with adsorbates such as CO or O,, H,O is a weakly chermsorbed species, on the borderline of physisorption. It is this weak interaction with the surface whtch makes intermolecular hydrogen bonding energetically favorable. As mentioned in section 2.2.2, hydrogen bond strengths in ice and water are typically 15 to 25 kJ/mol(4 to 6 kcal/mol or 0.2 to 0.3 eV). There is abundant evidence that water forms ice-like clusters on surfaces, similar to those shown m fig. 12 (p. 228) m which some water molecules form direct bonds to the surface and others are only held via hydrogen bonds to the first-layer molecules, forming a three-dimen- sional network. A possible cluster is shown m fig. 17. It is clear that a molecule which only forms two hydrogen bonds is bound by an energy at least comparable in magnitude to the chemisorption bond energy, so that formation of such clusters is certainly plausible. The tendency of water to form hydro- gen-bonded, three-dimensional islands at surfaces is a characteristic property which will recur in many aspects of our discussion. Evidence exists for the formation of hydrogen-bonded clusters on very many substrates, yet most theoretical models of surfaces to date treat isolated adsorbed H,O molecules. (The model of Paul and Rosen is an exception [64].) Intermolecular interaction is clearly very important, and so direct comparison between theoretical and expenmental work can, as yet, be made only m rare cases. Hydrogen bonding may be less prevalent for H,O on iomc surfaces, where the adsorption energy at specific sites is in some cases high enough to prevent clustermg (see section 7)."
