Atomic and Molecular Collisions Group



Main Page

Heavy Particle Collisions

Electron-Impact Ionization



Contact Info.

Data Tables

Charge Transfer

Electron Capture and Loss

Direct Scattering

Electron-Impact Ionization



The Atomic and Molecular Collisions Group is part of the Department of Physics and Astronomy at Rice University. We study the interaction of ions, atoms, and electrons with atoms and molecules. These interactions are not only of fundamental importance but are also essential to the detailed understanding of a broad range of large-scale physical systems such as, planetary atmospheres, astrophysical plasmas, gas discharge lasers, semiconductor processing plasmas, and fusion plasmas.

Our group has developed new techniques to study collisions of energetic ions and neutrals at an exceptionally detailed level. Much of the current program is directed toward understanding the basic physics of the collision processes that occur in the upper atmosphere and development of accurate data that are needed for modeling the atmospheres of the Earth and the other planets.

 Substorm picture

A magnetospheric substorm as seen by the Medium Energy Neutral Atom instrument on the IMAGE spacecraft. Interpretation of this type of space-based data requires knowledge of the underlying atomic collision processes.

This material is based upon work supported by the National Science Foundation under Grant Nos. 9726498 and 0108734 and by the Robert A. Welch Foundation. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the Robert A. Welch Foundation.


 Research Interests

Heavy Particle Collisions

The processes studied include elastic scattering of keV energy ions and neutrals, charge transfer of keV energy ions, and electron capture and loss reactions of keV neutrals. The focus of much previous work has been charge transfer of protons and oxygen ions with atomic oxygen. These processes are aeronomically very important and are also particularly difficult to deal with experimentally. Other work has involved measuring the differential charge transfer cross sections for state-selected oxygen ions. These studies are also directly applicable to the precipitation of energetic oxygen ions into the earth's upper atmosphere. Currently, experiments are underway to measure cross sections for electron capture and loss by O atoms in H2, N2, O2, and He.

Electron-Impact Ionization

Although the importance of electron-impact ionization has long been recognized, and the process has been studied experimentally since the 1920s, the total cross sections for many processes are only known to within a factor of two, and the cross sections for dissociative processes are known even less accurately. We have built an apparatus designed specifically to make accurate electron-impact ionization measurements. Over the past several years this apparatus has been utilized to study the following targets: He, Ne, Ar, Kr, Xe, H2, N2, O2, CO2, SO2, CH4, H2O, NO2, CO, CF4, SF6, NH3, and the methyl halides (CH3X, X=F, Cl, Br, I). Recent work has involved the simple alcohols (CH3OH, C2H5OH, C3H7OH), N2O, H2S, and CS2. Currently, CCl4 and CCl2F2 are being studied.


As is often the case in experimental physics, 'in house' development of technology is critical to the success of a project. Our group carried out some of the earliest work on the characterization and use of the position-sensitive detectors (PSDs) which are now an integral part of each of the apparatuses in our laboratory. More recently we have perfected a technique to use a commercial capacitance manometer at pressures much lower than previously thought possible. We have also worked on the developmentment of an accurate atomic oxygen sensor.



Lindsay photo

Dr. Bernard G. Lindsay
Senior Faculty Fellow
Stebbings photo
Professor Ronald F. Stebbings
Professor Emeritus



Recent publications

Publications 1990-1999

Publications 1980-1989



 Tabulated Data

Charge transfer cross sections

Electron Capture and Loss cross sections

Direct scattering cross sections

Electron-impact ionization cross sections



 Contact Information

Physics and Astronomy, MS 108
Rice University
6100 Main St.
Houston, TX 77005-1892
(713) 348 4932
(713) 348 5143

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Updated July 1, 2004