Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...p41b09t&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #P41B-09
Physics
0325 Evolution Of The Atmosphere, 0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707)
Scientific paper
Energetic charged-particle bombardment, dissociative recombination and photodissociation processes produce energetic recoil atoms which heat the thermosphere and can lead to escape from a planet affecting the evolution of the atmosphere. 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. Here we present our recent results for elastic collision and collisional dissociation cross sections relevant to Titan, Triton, Europa and the terrestrial planets [1,2]. Elastic and diffusion cross sections were calculated using both quantum mechanical techniques and the semiclassical JWKB approximation for the collision of ground state oxygen atoms in the energy range 1-10eV [2]. This involved calculation of phase shifts for each of the 18 molecular energy states of O2 which separate to two ground state O atoms. 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. Dissociation cross sections of N + N2 were calculated using a semiclassical method, in the energy range 0-30eV. This required treating the vibrational motion quantum mechanically while the rotational and the relative translational motion were treated classically. The evolution of the system was calculated by simultaneous propagation of the classical as well as the quantal degrees of freedom. The solution to the classical part was carried out by solving Hamilton equations of motion using an effective London-Eyring-Polanyi-Sato potential energy surface, calculated by Laganá et al [3]. Propagation of the quantal wavefunction was carried out by solving the time dependent Schrödinger equation using the split operator technique with the help of the fast fourier transform which was used to calculate the second derivatives arising from the kinetic energy operator. This work was supported by NASA's Planetary Atmosphere Program.
References 1. R.E. Johnson, M. Liu and C. Tully, Plant. Space. Sci., (2001), submitted.
2. C. Tully and R.E. Johnson, Plant. Space. Sci., (2001), in press.
3. A. Lagangá, E. Garcia and L. Ciccarelli, J. Phys. Chem. 91, 312-314, (1987)
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