title: Core-level spectra and molecular deformation in adsorption: V-shaped pentacene on Al(001).
abstract: By first-principle simulations we study the effects of molecular deformation on the electronic and spectroscopic properties as it occurs for pentacene adsorbed on the most stable site of Al(001). The rationale for the particular V-shaped deformed structure is discussed and understood. The molecule-surface bond is made evident by mapping the charge redistribution. Upon X-ray photoelectron spectroscopy (XPS) from the molecule, the bond with the surface is destabilized by the electron density rearrangement to screen the core hole. This destabilization depends on the ionized carbon atom, inducing a narrowing of the XPS spectrum with respect to the molecules adsorbed hypothetically undistorted, in full agreement to experiments. When looking instead at the near-edge X-ray absorption fine structure (NEXAFS) spectra, individual contributions from the non-equivalent C atoms provide evidence of the molecular orbital filling, hybridization, and interchange induced by distortion. The alteration of the C-C bond lengths due to the V-shaped bending decreases by a factor of two the azimuthal dichroism of NEXAFS spectra, i.e., the energy splitting of the sigma resonances measured along the two in-plane molecular axes.
authors.affiliation: ETSF, CNISM, Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, I-20125 Milano, Italy.
authors.forename: Anu
authors.initials: A
authors.lastname: Baby
authors.affiliation: ETSF, CNISM, Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, I-20125 Milano, Italy.
authors.forename: He
authors.initials: H
authors.lastname: Lin
authors.affiliation: ETSF, CNISM, Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, I-20125 Milano, Italy.
authors.forename: Gian Paolo
authors.initials: GP
authors.lastname: Brivio
authors.affiliation: CNR-IOM, Laboratorio TASC, Basovizza SS-14, Km 163.5, I-34149 Trieste, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Floreano
authors.affiliation: ETSF, CNISM, Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, I-20125 Milano, Italy; Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, I-20133 Milano, Italy.
authors.forename: Guido
authors.initials: G
authors.lastname: Fratesi
keywords: X-ray photoelectron spectroscopy (XPS); aluminum; density functional theory (DFT); near-edge X-ray absorption fine structure (NEXAFS); pentacene