Rate constants for the reactions of N⁺ and N₂⁺ with O₂ as a function of temperature (300-1800 K)

We have measured the rate constants for the reactions of N⁺ and N₂⁺ with O₂ from room temperature to 1600 and 1800 K, respectively. In the N⁺ reaction the rate constants increase with increasing temperature to 1000 K and level out at the collisional value above that. For the N₂⁺ reactions the rate constant decreases with temperature to 1000 K and increases above that value. Internal temperature dependences are derived by combining the data with previous drift tube measurements. The internal energy dependence of the N⁺ reaction appears to be a complicated function of vibrational, rotational, and electronic energy. In the N₂⁺ reaction, rotational and translational energy behave similarly, and O₂ vibrations are found to increase the rate constant dramatically. If all O₂ vibrations are involved, a factor of six enhancement is found. Alternatively, O₂ (ν = 2) allows exothermic production of O₂ + (a⁴Π_u). If the enhancement is due to this channel, then a factor of 20 enhancement is derived.