Cross Sections: Ion and Atom Collisions with Neutrals

    This archive contains cross section data of interest to modeling and simulations of the behavior of the exobase region of an atmosphere gravitationally bound to a planet or a planetary satellite. These may be used to describe thermal or plasma induced escape or to describe scattering processes occurring in a planetary torus consisting of neutrals and ions. The cross-section data are made available for use in various Monte Carlo modeling of these regimes, either ballistic modeling or molecular kinetic simulations, essentially numerical solutions to the Boltzmann equations. This work was funded by PDART program and was led by Bob Johnson and Hayley Williamson.

    This PDS4 bundle contains certain energy dependent cross sections that have been measured or calculated for use in modeling planetary atmospheres. The data presented here are not complete but can be supplemented by cross section models that can be estimated from online software and data stored on other web sites. Most of the data are for total reaction cross sections, with some from data-constrained models for differential cross sections that are needed for determining the probabilities for scattering into various angles for a given process. The angular scattering is discussed below as well as some methods for modeling or extrapolating cross sections. This work follows the methods discussed in Johnson (1990).

    The data relevant to upper atmosphere on various bodies vary considerably depending on the content of the upper atmosphere. For the giant planets these are typically H, H2, and He that interact with each other, their ions, and trace species. For the terrestrial planets and related small bodies, nitrogen, oxygen, and carbon species typically dominate. These molecules can be strongly gravitationally bound or even rapidly escaping as in a comet. Because of this, many useful websites have been constructed for relevant planetary objects. These contain cross-section data that supplements what is in this archive. A list of astrochemistry databases can be found at astrochem at the below link, which includes astronomical databases, grains and ices, chemical kinetics and reaction rates, and gas phase spectroscopy. (

    Access to the Data
    Bundle (hot_ion_atmos_escape) - Root directory for the bundle.


    Document – User Manual (cross_section_data_node.pdf)

    Data Derived - Data organized by subdirectory of chemical species and by reaction within the subdirectories.