Figure 1.

Energy diagrams of Stokes, Rayleigh, and anti-Stokes Raman scattering. Photons from the excitation source collide with the molecule, promoting the molecule to a short-lived virtual state, whereby it instantaneously emits energy and relaxes back to the lowest vibrational state with identical frequency to the incident light (Rayleigh), has a net increase in energy (Stokes), or has lost energy (anti-Stokes) [from Lupoi, “Developments in enzyme immobilization and near-infrared Raman spectroscopy with downstream renewable energy applications” (2012). Graduate Theses and Dissertations. Paper 12732.].