Effect of magnetic dipole coupling on optical binding energies between molecules

Abstract

Within the framework of molecular quantum electrodynamics, the method of induced multipole moments is used to compute the laser-induced intermolecular energy shift between an electric dipole polarizable molecule and a magnetic dipole susceptible molecule, and between two magnetic dipole polarizable molecules. The physical viewpoint adopted in the calculation is one in which an applied electromagnetic field induces molecular multipole moments in each entity, which couple via the retarded resonant multipole-multipole interaction tensors. Expectation values taken over the ground electronic states of the material system, and a radiation field state containing n photons, leads directly to the coupling energy. Results are obtained for external radiation in a fixed orientation relative to the internuclear axis, with a thorough polarization analysis being carried out for linearly and circularly polarized radiation propagating in directions parallel and perpendicular to the separation distance vector, as well as for a freely tumbling molecular pair. Comparison is made with field-induced discriminatory energy shifts occurring between optically active molecules – which also involve coupling of electric and magnetic dipole moments, and the leading contribution to optical binding forces arising within the electric dipole approximation.