Electron collisions with atoms and molecules are the major physical interaction determining the behaviour of all plasmas. Low energy electron collisions with molecules occur naturally in a number of astrophysical environments, in lightning bolts and within the body as a result of radiation damage. From a technical prospective such collisions are important in many applications including lighting, spark plugs and lasers. Furthermore electron induced reactions in both gaseous and condensed phases initiate and drive the basic chemical processes in different regimes from industrial plasmas to damage in living tissues. For example, electron induced reactions underpin most of the multi-billion dollar modern superconductor industry since it is those reactive fragments produced by electron impact of the etching gases that react directly with the silicon substance.
For many electron molecule problems it is difficult to make the relevant measurements in the laboratory. There is thus an increasing demand for computational procedures for obtaining reliable estimated cross section and rates for key processes. These are probably three state-of-the-art ab initio methods for treating low energy electron molecule collisions including electronic excitation. These are the Kohn variational method, the Schwinger variational method and R-matrix method. (You can find out more about R-Matrix method here)
Most advanced and most widely used R-matrix codes are the UK molecular R-matrix codes. These have been developed over a period of about 30 years from a number of scientists based at Queen’s University Belfast, Daresbury Laboratory, Royal Holloway College and, most recently, University College London.
The UK R-matrix codes are very flexible. Besides the basic electron collision problem they have been adapted to find (diffuse) bound states, compute differential and momentum transfer cross sections, treat rotational and vibrational excitation, obtain resonance parameters, quantum defects and branching ratios, treat dissociative recombination both using a complete non-adiabatic method and in tandem with multichannel quantum defect theory, study photoioniosation and processes in intense laser fields, and collisions with molecules physisorbed on surfaces. The codes have recently been extended to treat higher energies, larger molecules, electronically and more challenging problems.
The codes are freely available, see this page, but can only be used successfully by experienced scientists. Quantemol-N software system has been developed to address this problem: it both gives an expert interface for non specialists to perform ab initio electron-molecule scattering calculations and also provides training tool for those whishing to learn about such calculations.
