DICATIONIC STATES OF HYDROCARBONS AND A STATISTICAL APPROACH TO THEIR AUGER-SPECTRA

The valence doubly ionized states of acetylene and ethane are computed and discussed, complementing previous investigations on other hydrocarbons via the Green's function method. The vertical double ionization potentials are used for the interpretation of the Auger spectra of the molecules. The analysis is performed by employing a simple statistical approach to the Auger rates where the states are weighted by their two-hole components. For all hydrocarbons studied the resulting theoretical spectra exhibit maxima in good agreement with the experimental Auger peaks and reproduce the essential features of the experimental spectra. Strong final-state correlation effects are found for acetylene, ethylene, and benzene. They lead to a breakdown of the molecular orbital picture of double ionization which seems to be a typical phenomenon for unsaturated molecules. This phenomenon manifests itself in the Auger spectrum by the appearance of a high density of dicationic states which cannot be described in the independent-particle approximation. By contrast, the Auger spectrum of ethane is found to be dominated by the appearance of main states accompanied by weak satellite states at high energy. There is a correspondence between many-body effects in the Auger spectrum and the chemical bond. General aspects of correlation effects in dicationic states are discussed and related to the case of singly ionized states. © 1990 American Institute of Physics.