Kinetics of associative detachment of O− + N2 and dissociative attachment of e− + N2O up to 1300 K: chemistry relevant to modeling of transient luminous events

Abstract

The rate constants of O⁻ + N₂ → N₂O + e⁻ from 800 K to 1200 K and the reverse process e⁻ + N₂O → O⁻ + N₂ from 700 K to 1300 K are measured using a flowing afterglow – Langmuir probe apparatus. The rate constants for O⁻ + N₂ are well described by 3 × 10⁻¹² e^{−0.28 eV kT−1} cm³ s⁻¹. The rate constants for e⁻ + N₂O are somewhat larger than previously reported and are well described by 7 × 10⁻⁷ e^{−0.48 eV kT−1} cm³ s⁻¹. The resulting equilibrium constants differ from those calculated using the fundamental thermodynamics by factors of 2–3, likely due to significantly non-thermal product distributions in one or both reactions. The potential surfaces of N₂O and N₂O⁻ are calculated at the CCSD(T) level. The minimum energy crossing point is identified 0.53 eV above the N₂O minimum, similar to the activation energy for the electron attachment to N₂O. A barrier between N₂O⁻ and O⁻ + N₂ is also identified with a transition state at a similar energy of 0.52 eV. The activation energy of O⁻ + N₂ is similar to one vibrational quantum of N₂. The calculated potential surface supports the notion that vibrational excitation will enhance reaction above the same energy in translation, and vibrational-state specific rate constants are derived from the data. The O⁻ + N₂ rate constants are much smaller than literature values measured in a drift tube apparatus, supporting the contention that those values were overestimated due to the presence of vibrationally excited N₂. The result impacts the modeling of transient luminous events in the mesosphere.