Theoretical studies of dissociative excitation in electon-molecule collisions

Dissociative electron-molecule collisions play a key role in a variety of plasma processes such as plasma-enhanced chemical vapor deposition and low-temperature plasma etching, as well as proposed plasma-enhanced waste remediation methods. Although the detailed modelling of these plasmas may require many reactions involving neutral radicals and ionic fragments, the key steps which initiate this chemistry frequently involve the electron impact dissociation of a polyatomic molecule into neutral fragments. Electron-molecule dissociation cross sections are notoriously difficult to measure, because it is hard to detect neutral fragments; indeed, the number of systems for which experimental measurements have been made is quite small. Advances in ab initio theory and computational methodology over the past few years have made it possible to evaluate these cross sections for small polyatomics from first principles, although the calculations can be computationally demanding. The author describes recent efforts in this area using the complex Kohn variational method. The author summarizes the salient features of the method and illustrates the presentation with several examples including H2O, Cl2, NF3 and HBr