Laboratory Studies of O2 Excited States Relevant to the CO2 Planets

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In the upper atmospheres of Venus, Earth, and Mars, molecular oxygen is dissociated into atomic oxygen by absorption of solar ultraviolet radiation. The oxygen atoms can then recombine through a 3-body interaction with another molecule to form molecular oxygen in an excited state. On Venus and Mars, the third molecule is carbon dioxide. The competition between photodissociation, recombination, and diffusive transport determines the atomic and molecular composition of the mesosphere and lower thermosphere. Accurate knowledge of the oxygen atom recombination processes is critical for modeling the diurnal behavior of the altitude profile of oxygen atoms and interpreting nightglow emissions from atomic oxygen, molecular oxygen, and hydroxyl. In this project, the Principal Investigator and a postdoctoral fellow will conduct laboratory experiments to study the yields of the excited molecular oxygen states generated following O-atom recombination in a carbon dioxide environment. An ultraviolet light pulse from an excimer laser will photoinitiate O-atom recombination in carbon dioxide, maintained in a temperature-controlled gas flow cell. Fluorescence and resonance enhanced multiphoton ionization (REMPI) techniques will detect excited oxygen molecules and determine the yields of the excited states produced following O-atom recombination and subsequent relaxation in carbon dioxide. These measurements are needed to quantify oxygen airglow in the upper atmospheres of Venus and Mars and to probe their atmospheric dynamics by remote sensing. The results will benefit modelers of planetary atmospheres and will enhance the scientific returns on past and future missions to Venus and Mars. Application of basic chemistry and physics to the study of collisional processes is also critical for understanding the operation of high-power chemical lasers. Finally, the project will contribute to the training and research experience of a postdoctoral fellow and summer undergraduate students.