The resonant Auger electron spectrum of C 1s(-1)pi(*) excited ethene: A combined theoretical and experimental investigation

The resonant Auger electron spectrum for ethene has been calculated with an ab initio approach using configuration-interaction energies and wave funct ions for the intermediate core-excited and final states. The transition rat es were determined by the "one-center approximation." The role of vibration al relaxation on the line shapes was described by a moment method which con siders the case of symmetric core holes and their localization due to the v ibrational relaxation of the core-excited state. The core hole localization is investigated in some detail and is found to be extremely efficient in t he C 1s(-1)pi* excited state of ethene. Another property of the core-excite d state is found to be the polarization of the valence electron density tow ard the core hole. We demonstrate this by using three different symmetric c onfiguration interaction representations and one nonsymmetric Hartree-Fock representation for this state. A modified improved virtual orbitals method is described and employed to obtain virtual orbitals which give a compact d escription of this effect. The theoretical spectra obtained in this way are compared with a measured spectrum and assignment of the structures in the spectrum to electronic configurations is made. We find strong configuration mixing in the higher excited final states which is evidence for the breakd own of the one-particle picture. (C) 2000 American Institute of Physics. [S 0021-9606(00)31213-2].