Expanded Energy Corrections up to Second Order

Expansion at long range gives rise to the typical R n dependence of the intermolecular interactions. The first components of the long-range intermolecular interaction were studied by the author and coworkers in two papers (Magnasco et al., 1988,1990b), where the first few coefficients of the R expansion were determined explicitly for atom-atom, atom-linear molecule, and linear molecule-linear molecule systems. 

In the first order of perturbation theory, the expanded electrostatic energy gives rise to what is known as the interaction between permanent 

5 These angles are simply related to the Euler angles describing the rotation of a rigid body (Brink 

The two papers cited above also give explicit expressions for the polarization (induction) energies between polar molecules. They are expressed in terms of permanent moments and static polarizabilities of the interacting molecules. Both are observable quantities that can be measured by experiment. 

The expanded dispersion energy involves the interaction between induced moments on two atoms, the leading term describing the interaction between induced dipoles on A and B being  

An alternative, yet equivalent, expression for the dipole dispersion constant is the Casimir-Polder formula (Casimir and Polder, 1948)  

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Expanded Energy Corrections up to Second Order The Two-state Model of Long-range Interactions... 

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