In the literature of Fe(II) spin-crossover systems, the Franck-Condon factors between the two spin states are often approximated using the wavefunctions of the harmonic oscillator with a frequency that corresponds to the breathing mode, (the single configurational coordinate for the transition). The quintet states are produced by shifting the singlet potential horizontally along the SCC, and vertically by the energy gap ∆EHL. Consequently, the quintet wave functions are those of the singlet, shifted accordingly by the reduced energy gap, p = ∆E 0 HL /hω. Then, for calculating F (T ) the overlap of the m th quintet wavefunction with the (m + p) th singlet wavefunction needs to be considered: