Figure 1.

a) Transition diagram for Raman scattering (ν₀ is the laser frequency, and ν_s is the scattered frequency; ν_v is the frequency of a vibrational transition). When the laser wavelength is tuned to resonance with an electronic transition (S₀ − S₁), the Raman intensity is enhanced for chromophore vibrations. b) Absorption spectrum of HbCO, highlighting the heme, aromatic residue and amide absorption bands. c) Laser excitation within these bands yields RR spectra dominated by the respective chromophores.