On the manifestation of Casimir effects in intermolecular interactions via the method of induced moments

Abstract

A versatile, alternative method for calculating long-range interactions between atomic and molecular systems within the framework of non-relativistic quantum electrodynamics is the induced multipole moment approach. In the present contribution it is employed to compute the dispersion energy shift between a pair of neutral polarizable molecules in either ground or excited electronic states, and the change in mutual interaction energy caused by the action of an intense external radiation field. In this method the moments induced at each centre are coupled to each other via the resonant electric dipole-electric dipole interaction tensor, giving rise to an energy shift. On evaluating the expectation values for states corresponding to (i) both molecules in the ground state and the field in the vacuum state, (ii) both species excited and the field containing no photons, and (iii) both molecules in the ground state with the field containing I photons, respectively result in energy shifts for each of the three processes described above. For the modification of the dispersion interaction by laser light, two distinct mechanisms are identified. One, the dynamic contribution, is proportional to the polarizability of each molecule, and a second, the static term, involves the product of the static moment at one centre and the molecular first hyperpolarizability of the other entity. In both cases the energy shift has a linear dependence on radiation field intensity. After molecular averaging, the static contribution is found to vanish.