Experimental and theoretical studies of the N₂⁺+O₂ reaction

A technique by which ions are formed by resonance-enhanced multiphoton ionisation (REMPI) and detected by laser-induced fluorescence (LIF) has been employed to measure the kinetics of the N₂⁺+O₂ reaction over the pressure range 5-484 Torr He at 296 K. Within this pressure range, measured rate constants for the reaction are found to increase by a factor of ~2. It is well-established that the reaction proceeds predominantly by charge transfer at low pressure (<1 Torr). At higher pressures, the increase in rate constant for the reaction implies an increasing importance of the stabilisation of [N₂·O₂] ⁺ complexes. However, the observed dependence of rate constants on pressure provides good evidence that charge transfer also proceeds via [N ₂·O₂]⁺ complexes and that the contribution of charge transfer to the observed rate constant is pressure-dependendent. Extensive electronic structure calculations conducted at the QCISD/6-311G(d) level are presented and provide a framework to rationalise the experimental results.