Quantum electrodynamics with nonrelativistic sources. III. Intermolecular interactions

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Abstract
The multipolar formalism for a system of molecules developed in paper I (first preceding paper) is applied to a molecular pair to calculate the rate of energy transfer and intermolecular potential energies. In these calculations, one of the molecules is treated as passive when placed in the Maxwell field of the other. The electromagnetic field is calculated with the use of the Heisenberg picture as in paper II (second preceding paper). For resonance transfer between identical molecules, it is sufficient to consider the first-order fields to obtain the Förster rate. For nonidentical molecules, the probability of excitation transfer as a function of time is found with the use of the Heisenberg fields. A noteworthy feature of the calculations of dispersion energy is that with the use of electromagnetic fields, correct to quadratic terms in the transition moments, the complete Casimir-Polder intermolecular potential energy can be obtained by the consideration of one molecule as a test polarizable body in the field of the other.