Kinetics and photochemistry of NO3. Part 2.—Kinetics of the reaction NO2+ NO3+ M

Abstract

This paper describes kinetic investigations into the reactions NO₃+ NO₂+ M → N₂O₅+ M (2), N₂O₅+ M → NO₂+ NO₃+ M (–2) with M = O₂([M]=ca.(2–6)× 10¹⁸ molecule cm^–3; T= 298 K).

The NO₃ radical was generated by injecting NO₂ into a recirculated flow of ozone, and concentrations measured from the optical absorption at λ= 662 nm. Variation of [NO₃] with [NO₂]₀(the injected concentration) for [NO₂]₀ between ca. 1 × 10¹² and 10 × 10¹² molecule cm^–3 shows that k₂[M]=(2.0 ± 0.8)× 10^–12 cm³ molecule^–1 s^–1 at [M]= 2.7 × 10¹⁸ molecule cm^–3. The reaction appears to be near its second-order limit at this concentration. For [NO₂]₀≳ 10¹⁴ molecule cm^–3, the measured concentrations of [NO₃] show that k_–2[M]=(1.0 ± 0.6)× 10^–1 s^–1, corresponding to an equilibrium constant K=k_–2/k₂=ca. 5 × 10¹⁰ molecule cm^–3, in agreement with other determinations. A comparison is made of the individual rate constants with previously published values for M = N₂.