Mathematics – Probability
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p11a1248f&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P11A-1248
Mathematics
Probability
5405 Atmospheres (0343, 1060), 5435 Ionospheres (2459), 5704 Atmospheres (0343, 1060)
Scientific paper
Dissociative recombination of O2+ ions is the most important photochemical escape mechanism for oxygen atoms from Mars at the current epoch. We construct here models of the Martian thermosphere/ionosphere for low and high solar activities, and determine the rate of O2+ dissociative recombination (DR) as a function of altitude for each model. Using a Monte Carlo method, we compute the probabilities of escape for 16O and 18O atoms and compare them to see if there is a significant isotope effect. The escape probability for 18O atoms is expected to be less than that of 16O atoms, partly because 18O is released with less energy in DR of 34O2+ than that of 16O in DR of 32O2+, and its escape energy is larger. This isotope effect, which is inherent in the mechanism, is independent of the fractionation that exists between the homopause and the exobase. The energy distribution of O produced in O2+ DR is determined by the values of the ion and electron temperatures at a given altitude, and by the channels by which the DR proceeds. This energy distribution will be computed using a Monte Carlo method as a function of altitude from 100 to 400 km. Because the isotopes of O are found not to be fractionated in the Martian atmosphere relative to earth, a significant reservoir of O that can exchange with the atmosphere is implied. We also compute the total rates of photochemical escape of 16O from the Martian atmosphere for high and low solar activity models and compare them to the results of the many other investigators who have examined this escape mechanism.
Fox Lewis J.
Hać Aleksander B.
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