the interaction of systems of charged particles widely separated from one another, defined by the presence in the systems of what is called a quadrupole moment. If the electric charge or the dipole moment of a system differs from zero, the quadrupole interaction can usually be neglected.
The energy of quadrupole interactions for atoms (which have no dipole moment) falls off with the distance R by 1/R5, while the energy of the interaction of the dipole moments induced in these atoms by their mutual polarization varies with distance by 1/R6. Therefore, the quadrupole interaction of atoms is predominant at large distances. The quadrupole moment of atoms can be computed by means of quantum mechanics.
Many atomic nuclei in which the electric charge distribution does not have spherical symmetry have a quadrupole moment. Quadrupole interaction plays an important role in nuclear physics when a nucleus with zero dipole moment is excited by the coulomb field of charged particles bombarding it. Nuclear quadrupole moments are determined experimentally.
G. IA. MIAKISHEV