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C. Tully, M. Liu, R.E. Johnson (University of Virginia), V. Shematovich (Institute of Astronomy, Moscow)
Energetic charged-particle bombardment, dissociative recombination and photodissociation processes produce a hot corona and can cause escape on many planetary atmospheres. In describing these processes by Monte Carlo methods many of the critical cross sections are not available in the energy range of interest, a few eV to 1 keV. This is especially the case if one of the targets is a molecule. Earlier we gave results for dissociation of CO2 relevant to Mars (1). Here we present our recent results for elastic collision and collisional dissociation cross sections relevant to Titan, Triton, Europa and the terrestrial planets.
We carried out a detailed quantum mechanical calculation for O + O from 1eV to 10eV using all of 18 ground-state potentials and compared the results to simple models based on average potentials (2). For an O thermosphere the total elastic cross section is close to that typically assumed but the escape depths are shown to be larger than those typically used. In addition, we used laboratory data to create semi-empirical pair potentials to calculate collisional dissociation cross sections (3) for N + N2 for use at Titan (4) and for O + O2 for use at Europa (5). The latter have been incorporated into models of those atmospheres.
(1) R.E. Johnsn and M. liu, 1998, J. Geophys. Res. 103, 3639-3647
(2) C. Tully and R.E. Johnson PSS submitted to Plant. Sp. Sci.
(3) M. Liu, C. Tully, R.E. Johnson PSS to be submitted to Plant. Sp. Sci.
(4) V. Shematovich, C. Tully, and R.E. Johnson to be submitted
(5) V. Shematovich and R.E. Johnson ASR to be submitted to Ast. Phys. Rev.