Gas phase kinetics of the reactions of Na and NaO with O3 and N2O

Abstract

A fast flow reactor, with an oven source and resonant fluorescence detection, was used to study the kinetics of Na atoms in the gas phase. The rate constant for Na+O₃ is (7.3±1.4)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ at 286 K and NaO+O₂ is the predominant product channel. The rate constant for Na+N₂O over the temperature range 240 to 429 K is (3.7±0.9)×10⁻¹⁰ exp[(−1690±180)/T] cm³ molecule⁻¹ s⁻¹. The kinetics of the NaO radical were measured directly. NaO is made in the flow tube by the reaction Na+N₂O → NaO+N₂ with N₂O in large excess. NaO is detected by conversion to Na atoms in the detection region by NaO+NO → Na+NO₂. NaO+O₃ has two exothermic product channels, Na+2O₂ and NaO₂+O₂. The rate constants are ∼5×10⁻¹¹ and (1.8±0.4)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ at 296 K, respectively. Upper limits for NaO+N₂O →Na+N₂+O₂ and NaO+N₂O → NaO₂+N₂ are 1×10⁻¹⁶ and 2×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹, respectively. The rate constant for NaO+NO → Na+NO₂ is ∼1.5×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Since wall collisions remove NaO with near unit efficiency, NaO diffusion coefficients can be measured. D_NaO,He =640±340 cm² Torr s⁻¹ and DNaO,N₂O =48±24 cm² Torr s⁻¹ at 295 K. The error limits in all cases represent the 95% confidence level, including an estimate of systematic errors.