Energy Transfer in Collisions between Carbon Dioxide and Oxygen Atoms

Infrared absorption and emission by atmospheric constituents play a crucial role in determining the atmospheric temperature profiles of Earth and the other terrestrial planets, Venus and Mars. Carbon dioxide is a key contributor to the global energy balance of all three planets, mainly through its vibrational bending mode, CO2(nu2), which emits radiation near 15 micrometers (667 cm-1). This emission is a key cooling mechanism for the middle and upper atmospheres of these three planets. Accurate knowledge of the excitation mechanism for CO2(nu2) and the corresponding rate is crucial for reliable modeling of these atmospheric layers.

The key process controlling the coupling of the 15-micrometer radiation with the heat reservoir is excitation/quenching in collisions of CO2(nu2) with thermalized atomic oxygen in its ground state, O(3P). This process is poorly understood despite numerous studies over the past several decades. Unacceptably large discrepancies by factors of 3-4 exist between laboratory rate constant determinations for O-atom excitation/de-excitation of CO2(nu2) and the corresponding values retrieved by analyses of space-based atmospheric observations.

We present a progress report on our efforts to combine space-based observations, atmospheric modeling calculations, and laboratory experiments to resolve the long-standing problem of CO2(nu2) + O collisions as a source of the 15-micrometer emission.

This research is supported by the US National Science Foundation Aeronomy Program (Grants AGS-2125760 and AGS-2312191/2312192).