NEXAFS spectroscopy has potential for study of packing and order in organic materials but only if intermolecular effects are understood. This work studies how π-π interactions between adjacent unsaturated groups affect their NEXAFS spectra, with a broader goal of building a general understanding of the role of intermolecular effects in NEXAFS spectroscopy. These effects are examined using paracyclophane (PCP) molecules, in which the benzene-benzene separation distance is controlled by varying the length of the alkyl groups separating the benzene rings. NEXAFS spectroscopy and density functional theory (DFT) simulations are used to examine spectroscopic changes related to the strength of these π-π interactions. A characteristic red shift is observed as adjacent benzene rings get closer together. This shift is attributed to Coulombic and orbital interactions between the adjacent benzene rings, mediated through overlapping π/π* orbitals.

The near edge X-ray absorption fine structure (NEXAFS) spectra of orthorhombic single crystals of noctacosane (n-C 28 H 58 ), recorded at room temperature (298 K) and at cryogenic temperatures (93 K), show distinct differences. The characteristic carbon 1s → σ* C−H band in the NEXAFS spectrum of n-C 28 H 58 is broader and has a lower-energy onset in its room temperature spectrum than in its NEXAFS spectrum recorded at cryogenic temperatures. Density functional theory simulations show that nuclear motion and molecular disorder contribute to the observed spectral broadness and are the origin of the low-energy onset of the C−H band in the room temperature spectrum

Linear Dichroism in Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is a useful tool for studying molecular orientation and for clarifying spectroscopic assignments. n-Alkane molecules can form single crystals with different polymorphs; orthorhombic and monoclinic in the case of even chain lengths between n-C28H58 and n-C40H82. These polymorphs exhibit different linear dichroism in their NEXAFS spectra; in particular a backbone-oriented transition contributes to the low-energy "C-H" band in the monoclinic polymorph.