Franck-Condon Factors Each component of the overall vibronic coupling can be terms in terms of either an electronic-nuclear or electronic-vibrational coupling terms. The product overlap term is known as the Franck-Condon factors , and effectively dictates the degree of coupling a given mode has with respect to its degree of overlap with all other modes. As far as determining which of these modes are participating and which are preventing reversibility, it needs to be performed for each physical case, and is therefore phenomenological. However, this can be obtained from experimental data . The electronic-nuclear component to Equation 41 is cast in the same from as Equation , while the electronic-vibrational component can be cast using harmonic oscillator functions, shown as :