The C 1s NEXAFS spectrum of benzene below threshold:: Rydberg or valence character of the unoccupied σ-type orbitals

High-resolution C 1s near edge X-ray absorption fine structure (NEXAFS) spectra of benzene and benzene-d(6) were measured and compared with the results of state-of-the-art density functional theory (DFT) calculations demonstrating excellent agreement. The spectrum below threshold is dominated by four resonances, each two of them with sigma and pi-type final-state orbitals. The pi-type resonances have been ascribed in previous work unanimously to antibonding valence orbitals while the character of the sigma-type resonances is still the subject of discussion. Based on the present theoretical results and the observed vibrational fine structures both sigma-type orbitals are assigned to be valence type with minor admixtures of Rydberg character. (C) 2004 Elsevier B.V. All rights reserved.