Theory


Electron-molecule collision processes lead to both chemical and physical changes of matter in environments associated with radiation chemistry, stability of waste repositories, plasma-enhanced chemical vapour deposition (CVD), the lighting industry and plasma processing of materials for microelectronics.

In industry, CO2 lasers require electron impact excitation of vibrational and rotational states of the CO2and N2 to lase (Demaria 1979); hence an accurate knowledge of the relevant cross-sections is necessary for modelling and optimisation of the laser system.

In material science, electron scattering is used to probe the structure of materials such as molecular crystals (Dorset 1996).

The molecules used to etch semiconductor materials do not react with silicon surfaces unless they are subjected to electronic collisions to produce highly reactive radicals and ions in the low-temperature plasmas used in plasma etching and in plasma-enhanced chemical vapour deposition.

Electrons in radioactive and chemical waste are responsible for much of the chemistry that determines how these chemicals age and change.

Electron collisions create the reactive molecular fragments in the plasma devices which are used to destroy undesirable compounds or remediate NOx in combustion exhaust.

Collisions of low-energy electrons with molecules control many aspects of the environment and modern technologies. For example:

  • Initiating plasma etching processes.
  • Controlling the action of many lasers.
  • Controlling the ignition of internal combustion engines.
  • Determining edge effects in fusion plasmas.
  • Causing radiation damage in biological tissue.
  • Dictating the behaviour of the earth’s ionosphere.

Measurements of these collisions are both expensive and difficult to perform, and their theoretical determination requires the use of sophisticated procedures based on the application of quantum mechanics.

The Quantemol-N code provides an expert interface for driving the highly sophisticated UK molecular R-matrix code. By specifying a few easily determined molecular parameters the user can obtain parameters including collision cross sections, excitation cross sections and rates for electron collisions with molecules specified by the user.