Kinetics and photochemistry of NO 3 . Part 2.—Kinetics of the reaction NO 2 + NO 3 + M

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.