Re-analysis of the K-shell spectrum of benzene

The carbon K-shell spectrum of gaseous benzene has been recorded by inner-s hell electron energy loss spectroscopy (ISEELS) under electric-dipole condi tions (2 keV, small angle) with a resolution of 0.17 eV. Ab initio configur ation interaction calculations performed in the frame of the equivalent cor e model have helped in the assignment of the experimental spectrum. They em phasize the importance of the multi-configurational approach and the role o f the Rydberg orbitals in the assignment of some features. The band located at 289.09 eV is assigned to Rydberg excitations and a 3 pi* transition mix ed with doubly excited configurations, and not to an anti-bonding (C-H) tra nsition as suggested previously. Because of a large 3s/3d character of the (C-H)* orbital, the corresponding peak appears above the ionization thresho ld. The 293.8 eV band contains in-plane resonances and very likely also sev eral doubly excited states with a 3 pi* contribution. (C) 2000 Elsevier Sci ence B.V. All rights reserved.