Determination of the absolute rate constant for the reaction O + NaO → Na + O 2 by time-resolved atomic chemiluminescence at λ= 589 nm [Na(3 2 PJ)→ Na(3 2 S 1/2 )+hν]

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We present the first laboratory measurement of the absolute second-order rate constant for the overall removal of O(2 3PJ) by NaO: [graphic omitted] k2=k2a+k2b. 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 2PJ)→ Na(3 2S1/2)+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=k2b/(k2a+k2b) 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.