Technical Note: A new mechanism of 15 μm emission in the mesosphere-lower thermosphere (MLT)

Abstract

Abstract. Accurate knowledge of the rate as well as the mechanism of excitation of the bending mode of CO2 is necessary for reliable modeling of the mesosphere-lower thermosphere (MLT) region of the atmosphere. Assuming the excitation mechanism to be thermal collisions with atomic oxygen the rate coefficient derived from the observed 15 μm emission by space-based experiments differ from the laboratory measurements by a factor of 2–4. It is proposed that thermal collisions with N2, mediated by a near-resonant rotation to vibration energy transfer process, excite bending mode of CO2 by transferring energy from high rotational levels of thermal N2. Analogy with the excitation of the bending mode of CO2 by H2O, a process important in CO2 lasers, mediated by a near-resonant rotation-to vibration energy transfer process lends credibility to the hypothesis which has yet to be tested by direct calculations.