Linear dichroism in X-ray absorption spectroscopy of strongly chemisorbed planar molecules: role of adsorption induced rehybridisations

• Published in: Surface science 1995-11, Vol.341 (3), p.L1055-L1060
• Main Authors: Mainka, C., Bagus, Paul S., Schertel, A., Strunskus, T., Grunze, M., Wöll, Ch
• Format: Article
• Language: English
• Subjects: Applied sciences; Benzene; Chemisorption; Chemistry; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; General and physical chemistry; Impurity and defect levels; energy states of adsorbed species; Metals. Metallurgy; Near edge extended X-ray absorption fine structure (NEXAFS); Physics; Platinum; PMDA; Solid-gas interface; Surface and interface electron states; Surface physical chemistry
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(95)00795-4

Dipole selection rules require the π*-resonances, which dominate X-ray absorption spectra for planar aromatic molecules, to have zero intensity for X-ray photons linearly polarized in the molecular plane. For molecules adsorbed in a flat geometry on metal surfaces, however, very often considerable intensities are observed for s-polarized light. We will present experimental and theoretical evidence that for two molecules, benzene and pyromellitic dianhydride (PMDA) adsorbed on Pt(111), this anomalously weak linear dichroism is not due to molecular disorder as assumed previously but arises from molecular rehybridisation caused by out-of-plane molecular distortions.