[Previous] | [Session 37] | [Next]
G. Stark (Wellesley College), K. Yoshino, P.L. Smith (Harvard-Smithsonian Center for Astrophysics), K. Ito (Photon Factory, Tsukuba, Japan)
We report preliminary measurements of carbon dioxide photoabsorption cross sections in the 106 to 120 nm region. CO2 is the principal constituent of the atmospheres of Mars and Venus. Its dissociation by ultraviolet solar radiation initiates the production of non-thermal atoms that may escape these atmospheres, and leads, through further photochemistry, to ultraviolet and visible airglow features. The analyses of recent high-quality VUV observations of emission features in the Martian atmosphere and the modeling of non-thermal escape mechanisms from the Martian and Venusian atmospheres are limited by poorly and incompletely characterized CO2 VUV photoabsorption cross sections.
We recently tested the feasibility of a new measurement program for CO2 absorption cross sections in the 91 to 120 nm region at 295 K and 195 K. Our preliminary results for the 106 to 120 nm region derive from that feasibility study. Our measurements, at a resolution of 0.05 Å, were carried out on the 3-meter normal-incidence vacuum monochromator on the BL-20A beam line at the Photon Factory synchrotron facility in Tsukuba, Japan. Two points are evident from the preliminary spectra: (a) there is significant spectral structure in the CO2 absorption cross section that is not resolved in earlier lower-resolution work, and (b) there is clear evidence of systematic underestimation of peak absorption cross sections for the strongest CO2 features in the existing literature - a consequence of inadequate instrumental resolution.
This work was supported by NASA grant NAG5-9059.
If the author provided an email address or URL for general inquiries,
it is as follows:
Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.