Some consequences of molecular symmetry in the theory of photoelectron angular distributions

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Abstract
The molecular photoelectron angular distribution is treated by regarding the ionization process as a coherent superposition of component transitions, each having specific molecular symmetry transformation properties. The symmetry‐related properties of the resulting contributions and the selection rules that govern their occurrence in some specific ionization models are examined, and a generally applicable rule is obtained requiring interferences between ionization components with appropriate molecular symmetry transformation properties to vanish identically. Application of molecular symmetry methods to the angular momentum transfer formulation leads to the development of methods for generating angular‐momentum‐transfer selection rules. These methods are applied to direct ionization in an orbital approximation for 40 symmetries and for the general case of an n‐fold rotational symmetry, and meaningful restrictions on the allowed values of the angular momentum transfer are shown to apply even to some low symmetry systems.