Near-Edge X-Ray Absorption Fine Structure Spectroscopy: A Probe of Local Bonding for Organic Gases Solids, Adsorbates, and Polymers

The near edge X-ray absorption fine structure (NEXAFS) of the carbon K -shell is shown to be a sensitive probe of certain types of bonds and functional groups in organic molecules, regardless of whether the molecules are: isolated in the gas phase, condensed, chem­ isorbed on a surface, or a long chain polymer. To demonstrate this principle, the K -shell excitation spectra of molecules containing similar bonds and/or functional groups are presented and compared in the gas phase, the solid state and adsorbed on surfaces. From a systematic study of molecules with increasing size, guidelines are established which allow the understanding of the NEXAFS spectra of macromole­ cules and polymers based on a simple building block picture. As exam­ ples we discuss the spectra of single layer Langmuir-Blodgett and thin polymer films on surfaces and show that they can be interpreted in like manner to those of simple isolated molecules. We also discuss limi­ tations of the building block approach arising from conjugation effects in molecules or band structure formation in three dimensional periodic solids.