Excitation of the CO fourth positive system by the dissociative recombination of CO₂⁺ions

The fourth positive system of CO [A ¹Π → X ¹Σ] has been excited in a static afterglow experiment by the dissociative recombination of CO2+ ions. From combined absolute optical and microwave measurements the specific recombination coefficient for exciting the CO (A → X) system was found to be (2−0.5+1) × 10−8 cm³/sec. This value represents approximately 5% of the total recombination coefficient (4.0 ± 0.5) × 10−7 cm³/sec measured in this experiment, implying that CO2+ dissociative recombination will contribute significantly to the excitation of the CO fourth positive system in the martian airglow. Corroborative electron heating experiments showed that the magnitude of the specific recombination coefficient decreased as the electron temperature was increased. Evidence was also found for the presence of vibrationally excited ions in the CO2+ plasma, a result which indicates that analogous laboratory studies on the dissociative recombination of O2+, N2+, and NO+ ions may have also involved vibrationally hot plasmas.