Relativistic Intermolecular Forces, Moderately Long Range

Abstract

The generalized Breit—Pauli Hamiltonian is used to give a systematic treatment of magnetic and other relativistic intermolecular energies through O(α²) (where α is the fine‐structure constant) for intermolecular separations, R, sufficiently large that the charge distributions of the two molecules do not overlap, but sufficiently small that R<λ/₀=(αΔε)⁻¹, where Δε is the excitation energy of the first allowed transition of one of the molecules. The theory is discussed in general and many types of interaction energies are obtained which depend on the spin and orbital angular‐momentum states of the molecules. The interaction of two nondegenerate atoms (L=0, S=0) is considered specifically. Of particular interest is an interaction‐energy term which varies as α²/R⁴.