Figure 3.

Illustration of the different conditions of resonance Raman. (A) Off-resonance Raman scattering condition, E_n – E_i ≫ ℏω₀, in which many excited electronic states contribute (virtual intermediate states). (B) Preresonance Raman scattering condition, where ℏω₀ approaches E_n – E_i, and the vibrational states of the lowest excited electronic state act as intermediate states. (C) Rigorous resonance Raman scattering condition, where E_n – E_i ∼ ℏω₀ and one particular vibronic state, |e⟩|ν⟩, dominates the scattering process. Reproduced with permission from ref (26). Copyright 2016 John Wiley & Sons, Ltd.