The resonance Raman spectrum of nitrogen dioxide

An Ar ⁺ laser induces strong resonance Raman scattering from NO ₂ pressured with a transparent gas. Using 5145 or 4965-Å excitation the vibration-rotation scattering is concentrated in ^qQ branches (∆ K = ∆ N = 0) with K = 0-8 or 9. Resonance enhancement affects the Q branches unequally, certain of the ^qQ_K being weak or missing. With 4880-Å excitation the ^qQ branches are accompanied by weaker ^δQ branches, where the presence of ∆ K = 2 transitions indicates that the B∼²B ₁ state contributes to the resonance enhancement. The transition from a resonance fluorescence spectrum at low gas pressure to resonance scattering at total pressures in excess of 1 atm is discussed in relation to theories of the time evolution of on- and off-resonant photon-molecule interactions.