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# Electron collisions

## Electron scattering from molecules

The molecular physics group studies the scattering of electrons from diatomic and polyatomic molecules using the R-matrix method. Applications include fusion plasma modelling (see with workshop on Electron-molecule Collision Data for Modelling and Simulation of Plasma Processing in 1998) and applications in astrophysics. Scattering cross-sections are computed as well as bound state energies of N+1 electron systems.

Some molecular data from our calculations can be found here. Our work uses the UK molecular R-matrix code. The figure illustrates the principle of the R-method.

The R-matrix method divides space in two regions:

 inner region: has similarities with the bound state electronic structure problem and the quantum chemistry codes ALCHEMY and Sweden-Molecule have been adapted to treat this region outer region: here the problem is formally similar to electron-atom collisions although in practice it is more complicated.

At low impact energies (<= 20eV) there are many processes that need to be considered:

 Electronic Excitation AB + e [image reference is broken] AB* + e Vibrational Excitation AB (v''=0) + e [image reference is broken] AB (v') + e Rotational Excitation AB (N'') + e [image reference is broken] AB (N') + e Dissociative attachment/recombination AB + e [image reference is broken] A- + B [image reference is broken] A + B- Elastic scattering AB + e [image reference is broken] AB + e Dissociative scattering AB + e [image reference is broken] A + B + e

Consider for example dissosciative recombination. The graph shows a plot of the potential energy against separation of the two H atoms for different reactions products. The red potential curve intersects one energy level of the black potential curve. An molecule in this state (H2+) can relax into the lower energy state of two H atoms. This is an example of dissociative recombination. The electron is used to excite the molecule into this energy level. Dissosciative recombination (DR) was discovered in the Earth's atmosphere to account for the destructive O2+ ions. It is a major destroyer of molecular ions. Especially both poles of the earth's magnetic field attract extraterrestial particles and force them to move along magnetic field lines. This particles cause a phemenon known as Northern Lights.

This work is performed as part of a UK collaboration supported by CCP2. The Collaborative Computational Project Two deals with Continuum States of Atoms and Molecules. Find out more about this and other programmes which are part of this framework on the CCP2 webpage.