Molecules interact at close range through intermolecular forces (the "van der Waals forces"), which cause minute shifts of the electron density distributions (relative the distributions of electrons when the molecules are not interacting). Intermolecular forces are repulsive at near range, where electron exchange forces dominate the interaction, and attractive at somewhat greater separations, where the dispersion forces are active. (If separations are further increased, all intermolecular forces fall off rapidly and may be totally neglected.) Repulsion and attraction are due, respectively, to the small defects or excesses of electron densities of molecular complexes in the space between the interacting molecules, which often result in interaction-induced electric dipole moments that contribute some to interaction-induced emission and absorption intensities. The resulting dipoles are referred to as exchange force-induced dipole and dispersion force-induced dipoles, respectively.