Determination of the absolute rate constant for the reaction O + NaO → Na + O2 by time-resolved atomic chemiluminescence at λ= 589 nm [Na(3 2PJ)→ Na(3 2S1/2)+hν]

Abstract

We present the first laboratory measurement of the absolute second-order rate constant for the overall removal of O(2 ³P_J) by NaO: [graphic omitted] k₂=k_2a+k_2b. NaO was generated at known concentrations in the presence of an excess of He in a slow-flow system by titrating N₂O with Na derived from a heat-pipe oven via the reaction Na + N₂O → NaO + N₂. Atomic chemiluminescence at λ= 589 nm [Na(3 ²P_J)→ Na(3 ²S_1/2)+hν] subsequent to pulsed irradiation was then monitored in the time domain following reaction (2b). Analysis of the chemiluminescence profiles yielded k₂(T= 573 K)=(3.7 ± 0.9)× 10^–10 cm³ molecule^–1 s^–1. The importance of this reaction in interpreting the mesopheric chemistry of sodium is considered in detail. An estimate of the branching ratio α=k_2b/(k_2a+k_2b) from the present measurements of ca. 1 % indicates a value considerably lower than that based on statistical considerations alone and used previously in computer models of the mesosphere.