Abstract

Vibrational excitation of ground‐state NO through collisions with oxygen atoms produces NO(v = 1) in the lower thermosphere, representing a significant source of atmospheric cooling through the subsequent 5.3‐μm radiative emission. A laser pump‐probe experiment has been used to measure the temperature dependence of the NO(v = 1)‐O vibrational relaxation rate coefficient kO(v = 1) in the 295–825 K range, along with updated measurements of kO(v = 1,2) at room temperature. The experiment employed a continuous wave microwave source to form O atoms, combined with photolysis of a trace amount of added NO2 to produce vibrationally excited NO. Oxygen atoms were detected through two‐photon laser‐induced fluorescence, cross‐calibrated against a normalized O atom signal resulting from photolysis of a known concentration of NO2. No temperature dependence was observed for kO(v = 1) to within the uncertainty in the measurements. The measured room temperature value of kO(v = 1) = (4.2 ± 0.7) × 10−11 cm2 s−1 is 75% larger than the value obtained previously in this laboratory, a significant difference at the 1σ level. The present value is preferred owing to an improved experimental technique. The atmospherically relevant NO(v = 0)‐O vibrational excitation rate coefficient can be derived from measured values of kO(v = 1) through detailed balance. The variable temperature measurements provide key information for aeronomic models of the lower thermospheric energy budget, infrared emission intensities, and neutral constituent densities.

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