Rotational branch analysis of the excitation of the fundamental vibrational modes of CO₂by slow electron collisions

At 2 eV, the simultaneous rotational-vibrational cross sections for the fundamental modes are found to be well described by the Born formula with just long-range interactions. However, this result is not obtained for pure vibrational excitation (Q branch) in the Raman-active Fermi diads. At 3.8 eV, the infrared-active nu 2 and nu 3 cross sections agree with a previous theory incorporating resonant and direct scattering coherently. Measurements of the Raman-active nu 1 mode indicate that the theories need to account for the Fermi resonance.