Here, E mn is assumed to be much larger than the average vibrational energy, which allows the simplification that only high-frequency normal modes need be analysed. In terms of a physical system, this can be thought of as a series of weakly coupled oscillators, where each oscillator exhibits roughly the same frequency, the energy of which corresponds to the energy of the highest frequency transition participating mode ω MAX . In this picture, the energy gap law can be cast as :