Question

Explain how the induced, orientation, and dipersion interactions trend between HCl, HBr, and HI. Why do the dipersion interactions increase from HCl to HI? Why do the orientation interactions decrease from HCl to HI? Why are induced interactions greatest in HCl and lowest in HI?

Answer 1

The first explanation of the attraction between noble gas atoms was given by Fritz London in 1930.^[2][3][4] He used a quantum-mechanical theory based on second-order perturbation theory. The perturbation is the Coulomb interaction V between the electrons and nuclei of the two monomers (atoms or molecules) that constitute the dimer. The second-order perturbation expression of the interaction energy contains a sum over states. The states appearing in this sum are simple products of the stimulated electronic states of the monomers. Thus, no intermolecular antisymmetrization of the electronic states is included and the Pauli exclusion principle is only partially satisfied.

London developed the method perturbation V in a Taylor series in , where is the distance between the nuclear centers of mass of the monomers.

This Taylor expansion is known as the multipole expansion of V because the terms in this series can be regarded as energies of two interacting multipoles, one on each monomer. Substitution of the multipole-expanded form of V into the second-order energy yields an expression that resembles somewhat an expression describing the interaction between instantaneous multipoles (see the qualitative description above). Additionally, an approximation, named after Albrecht Uns