Ionosphere‐exosphere coupling through charge exchange and momentum transfer in hydrogen‐proton collisions

Abstract

We examine the implications of a traditional assumption of exospheric physics, that collisions of hydrogen atoms and protons preferentially result in charge exchange with negligible momentum transfer. Initially adopted as a necessary convenience to accommodate limited computer resources in exosphere model calculations, this approximation results in a direct transformation of the proton velocity distribution into a hot component of neutral hydrogen. It leads to significant enhancements in both escape and in the formation of extended planetary coronae. With expanding computational facilities, the need for the approximation has passed. As the first step toward its replacement with a realistic, quantum mechanical model of the H‐H+ collision process, we calculate differential and cumulative cross sections for quantum elastic scattering of indistinguishable nuclei for a fine grid of encounter energies and scattering angles. These data are used to study the nature of ionosphere‐exosphere coupling through H‐H+ collisions, and to demonstrate that the distribution of velocities of scattered H produced in the traditional exospheric charge exchange approximation, as well as that arising from an alternative, fluid dynamics approach, leads to unacceptable abundances of coronal atoms in long‐term, highly elliptic trajectories.

Regge Oscillations in Integral Cross Sections for Proton Impact on Atomic Hydrogen

“…In this connection, note that these features were seen in the hyperspherical calculations of Igarashi and Lin [9] for HD where it was also shown that they could not be identified with resonances in the partial cross sections. Earlier calculations for H H and H D also showed the oscillations but did not identify their origin [5,6]. The main point of our work is to show that these features cannot be identified with structures in the partial cross sections, and that a representation of integral cross sections alternative to the partial wave representation is needed.…”

“…In this work we analyze oscillations in H H spin exchange and elastic scattering cross sections at energies in the range 0:01-1:0 eV [5][6][7] that are neither associated with specific partial waves nor are explained by stationary phase evaluations of the partial wave sum.…”

Energetic neutral atom imaging of comets

“…To not violate this assumption we only consider protons with energy larger than 50 eV [Hodges and Breig, 1991] in this work.…”

Heating and Ionization ofX‐Winds

“…In addition to the deÐnitive work of Hunter & Kuriyan (1977) for E [ 10~4 eV, the momentum transfer cross sections have been calculated by Hodges & Breig (1991) …”