where Λ s is the energy resonance defect between the initial and final states, and Γ ns is the relaxation width of the vibrational state n. The resonance energy defect is smaller than or equal to ∼100 cm -1 when both initial and final electronic states are in their zeroth-vibrational state . Green's functions were initially used to cast the harmonic and anharmonic vibrational terms since at the time alternative methods to model the aromatic C-H stretching modes were not available. Green's functions are applicable when coupling is comparably smaller than either Γ ns or Λ {n} . Lin noted that most of the electronic energy in internal conversion is transferred to the vibrational continuum rather than straight to phonon-based relaxation. Physically, this represents the case where non-radiative transitions originate from a Boltzmann distribution of vibrational levels. Another way to interpret this is that the electronic energy from the initial state is transferred via vibronic quanta to the final state .