Theoretical and Experimental Studies of O-CO2 Collisions

Details Theoretical and Experimental Studies of O-CO2 Collisions Theoretical and Experimental Studies of O-CO2 Collisions

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsa72a0514h&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SA72A-0514

Physics

0317 Chemical Kinetic And Photochemical Properties, 0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707), 0360 Transmission And Scattering Of Radiation, 1610 Atmosphere (0315, 0325), 6207 Comparative Planetology

Scientific paper

Infrared emissions near 15 μm from bending-mode vibrationally excited carbon dioxide molecules control the rates of radiative cooling in key altitude regions of the upper atmospheres of Venus, Earth and Mars. The critical limiting process is excitation of CO2(v2) in collisions with atomic oxygen. Laboratory measurements suggest rate coefficients about 3 times smaller than the values preferred by modelers. Our theoretical investigations have developed improved potential energy surfaces for O + CO2. A Diatomics-in-Molecules approach combines O-O and O-C repulsion and dispersion interactions, modeled by ab initio potential energy curves of the ArO molecule, with electrostatic interactions of the oxygen atom quadrupole moment with fractional charges on the CO2 molecule, corresponding to its permanent quadrupole and instantaneous dipole moments. Nonadiabatic matrix elements are calculated by integrals over products of bending wavefunctions versus the CO2 bond angle. Spin-orbit coupling is explicitly included. Results of Landau-Zener calculations will be presented. Calibration with ab initio O-CO2 potential energy surfaces as well as quasiclassical trajectory calculations are underway. The experimental approach is based on 248-nm photodissociation of ozone, followed by energy transfer of O(1D) to CO2(vib), whose time evolution is followed by resonance-enhanced multiphoton ionization (REMPI). Preliminary work on the CO2 REMPI spectrum will be presented. Supported by the NASA Planetary Atmospheres Program.

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