The Guggenheim-Smith equation gives this quantity 
The Guggenheim-Smith equation gives this quantity as proportional to the square root of the molar orientation polarizability. The direction of this vector quantity determines the kappa squared term in FRET. For a molecule, this quantity changes when it undergoes scissoring, wagging, or rocking. A selection rule for a quantum harmonic oscillator is that the integral of the operator for this quantity cannot be zero. The cross product of this quantity with electric field equals torque, and the dot product equals negative potential energy. The ratio of this quantity to the electric field has units volume and is called polarizability. A molecule is polar if this quantity is nonzero. For 10 points, name this quantity, measured in Debyes, that is the charge times the separation distance for two oppositely charged particles.
The Guggenheim-Smith equation gives this quantity as proportional to the square root of the molar orientation polarizability.
electric dipole moment [or transition dipole moment; do not accept "magnetic dipole moment"]