Potential surface, intermolecular interaction

P.R.P. Barreto, A.F. Albemaz, F. Palazzetti, A. Lombardi, G. Grossi, V. Aquilanti, Hyperspherical representation of potential energy surfaces intermolecular interactions in tetra-atomic and penta-atomic systems, Phys. Scr. 84 (2011) 028111. 

This section describes solid-gas surface processes on the surface monolayer adsorption, desorption, catalytic reaction, and surface diffusion. Non-ideal behavior of the systems is considered through the pair potentials of intermolecular interactions. A wide circle of experimental data can be... 

Brinck, T., J. S. Murray, and P. Politzer. 1992b. Surface Electrostatic Potentials of Halogenated Methanes as Indicators of Directional Intermolecular Interactions. Int. J. Quant. Chem., Quant. Biol. Symp. 19, 57. 

The inner and outer potential differ by the surface potential Xa — (fa — ipa- This is caused by an inhomogeneous charge distribution at the surface. At a metal surface the positive charge resides on the ions which sit at particular lattice sites, while the electronic density decays over a distance of about 1 A from its bulk value to zero (see Fig. 2.1). The resulting dipole potential is of the order of a few volts and is thus by no means negligible. Smaller surface potentials exist at the surfaces of polar liquids such as water, whose molecules have a dipole moment. Intermolecular interactions often lead to a small net orientation of the dipoles at the liquid surface, which gives rise to a corresponding dipole potential. 

These results suggest that the critical factor in the substrate-mediated intermolecular interactions which occur within the close-packed DHT layer is the inherent strong reactivity of the diphenolic moiety with the Pt surface. The interaction of adsorbates with each other through the mediation of the substrate is of fundamental importance in surface science. The theoretical treatment, however, involves complicated many-body potentials which are presently not well-understood (2.). It is instructive to view the present case of Pt-substrate-mediated DHT-DHT interactions in terms of mixed-valence metal complexes (2A) For example, in the binuclear mixed-valence complex, (NH3)5RU(11)-bpy-Ru(111) (NH 3)5 (where bpy is 4,4 -bipyridine), the two metal centers are still able to interact with each other via the delocalized electrons within the bpy ligand. The interaction between the Ru(II) and Ru(III) ions in this mixed-valence complex is therefore ligand-mediated. The Ru(II)-Ru(III) coupling can be written schematically as ... 

Fig. 5.1 A schematic projection of the 3n dimensional (per molecule) potential energy surface for intermolecular interaction. Lennard-Jones potential energy is plotted against molecule-molecule separation in one plane, the shifts in the position of the minimum and the curvature of an internal molecular vibration in the other. The heavy upper curve, a, represents the gas-gas pair interaction, the lower heavy curve, p, measures condensation. The lighter parabolic curves show the internal vibration in the dilute gas, the gas dimer, and the condensed phase. For the CH symmetric stretch of methane (3143.7 cm-1) at 300 K, RT corresponds to 8% of the oscillator zpe, and 210% of the LJ well depth for the gas-gas dimer (Van Hook, W. A., Rebelo, L. P. N. and Wolfsberg, M. /. Phys. Chem. A 105, 9284 (2001))...

The very high ionization potential and the low polarizability of the fluorine atom imply that fluorinated compounds have only weak intermolecular interactions. Thus, perfluoroalkylated compounds have very weak surface energies, dielectric constants, and refracting indexes. 

Principle of corresponding states. Intermolecular potentials, like the induced dipole surfaces, are functionals of the intermolecular interactions. The signatures of electron exchange, dispersion and multipole induction are clearly exhibited in both they have much in common. 

---