Dispersion energies of interaction between asymmetric molecules

A formula is derived that expresses the contribution of the electric dipole-quadrupole forces to the dispersion energy between two unexcited molecules possessing axial symmetry. The relative orientation of the symmetry axes is arbitrary and the molecules need not be identical. Our formula holds for the case that each molecule belongs to a substance whose optical dispersion curve is characterized by a pair of resonance frequencies. A few orientations of special interest are subjected to numerical analysis based on the experimental data for polarizabilities of some diatomic molecules. Thus estimates are gained of the magnitude of errors inherent in energy values computed as if spherical symmetry obtained.