Towards a detailed understanding of the NEXAFS spectra of bulk polyethylene copolymers and related alkanes

High energy resolution C 1s near-edge X-ray absorption fine structure (NEXAFS) spectra of ethylene-1-alkene copolymers with systematic variations in comonomer content and thus systematic changes in branch length, branching ratio, and degree of crystallinity are presented. Spectral changes of the σ*C–H/Rydberg and σ*C–C features in these ideal model systems provide unambiguous experimental evidence for intermolecular interactions with profound effects on the spectral intensity, but only very small energy shifts. Ab initio calculations reproduce the experimental results in detail. The intermolecular interaction observed suggests that interpretation of NEXAFS spectra based on calculations of isolated molecules can be insufficient even in relatively weakly interacting macromolecules.