Chemical Kinetics of the NaO (A 2Σ+) + O(3P) Reaction

Abstract

Recent evidence has shown that the mesospheric sodium nightglow, a chemiluminescent process which produces atomic sodium D-line radiation in the Earth's upper atmosphere, proceeds through the first excited (A 2Σ+) electronic state of NaO. The rate of D-line radiation production is proportional to the rate constant for the reaction of NaO(A 2Σ+) + O(3P) and its branching ratio to produce excited Na(2P) rather than ground-state Na(2S). The only previously published measurement of the NaO + O(3P) reaction rate and branching ratio was performed under slow flow conditions and almost certainly primarily represents the reaction of ground-state NaO (X 2Π). We present low-pressure measurements of the NaO + O reaction kinetics using an NaO source reaction known to produce NaO in the (A 2Σ+) state and determine the 290 K reaction rate constant to be (5.1 ± 1.8) × 10-10 cm3 s-1 and the branching ratio to produce Na(2P) to be 0.14 ± 0.04. New data on the termolecular rate coefficient for the reaction Na + O2 + He → NaO2 + He at 290 K are also presented.