Transition dipole moment
The transition dipole moment or transition moment, usually denoted d n m {\displaystyle \mathbf {d} _{nm}} for a transition between an initial state, m {\displaystyle m} , and a final state, n {\displaystyle n} , is the electric dipole moment associated with the transition between the two states. In general the transition dipole moment is a complex vector quantity that includes the phase factors associated with the two states.