Approaches to Measuring CO2(ν 2)-O Vibrational Energy Transfer

Details Approaches to Measuring CO2(ν 2)-O Vibrational Energy Transfer Approaches to Measuring CO2(ν 2)-O Vibrational Energy Transfer

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsa51a0769c&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SA51A-0769

Physics

0355 Thermosphere: Composition And Chemistry

Scientific paper

Preliminary experiments have been carried out with the goal of accurately measuring the vibrational relaxation rate of CO2(ν 2) by ground state atomic oxygen. Significant cooling occurs in the 70-120 km altitude region through efficient uppumping of vibrational ground state CO2 by ambient O atoms. Much of the nascently-excited CO2(ν 2) radiatively decays, converting a portion of the ambient kinetic energy into 15 μ m IR emission which escapes into space. However, the rate constant for the reverse CO2(ν 2)-O vibrational relaxation process is not generally agreed upon. In previous work, the rate constant was measured by photolyzing ozone in an O3-CO2-Ar mixture, both generating a high density of O atoms and slightly raising the gas temperature. The re-equilibration rate of the CO2 vibrational population was then monitored as a function of the O-atom density, using diode laser absorption in the 4.3 μ m region. In the present work, we are investigating a similar experiment utilizing the stable precursors NO2 and SO2 as alternatives to O3. We have also performed preliminary experiments in which the bend state of CO2 is selectively populated using stimulated Raman excitation. Finally, detection of the laser-excited CO2 vibrational populations has been performed using absorption of broadband IR radiation from a SiC lamp in conjunction with a Fourier transform spectrometer. We compare the advantages and disadvantages of using the FTIR technique versus diode laser detection.

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