Angular distribution of Auger electrons emitted by polyatomic molecules

A general theory is developed for the angular distribution of Auger electrons emitted by polyatomic molecules in the gas phase after ionization by electron impact. General formulae are derived which are useful as a basis for numerical calculations and for an analysis of experimental data. The Auger process is described using a two-step model. We suggest a parametrization of the molecular axis distribution function in terms of order parameters, which offers a convenient characterization of the anisotropy produced in the primary ionization. The process is discussed separately for non-degenerate point groups. In the latter case the description of the coherences produced in the primary process requires additional parameters, which have not been taken into account in previous formulations for polyatomics but which are important for any numerical calculation of angular distributions. Consequences of molecular symmetries are pointed out for some examples. (author)