Spectroscopic analysis of small organic molecules: A comprehensive near-edge x-ray-absorption fine-structure study of C6-ring-containing molecules

Abstract

We report high-resolution C 1s near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the C6-ring-containing molecules benzene (C6H6), 1,3- and 1,4-cyclohexadiene (C6H8), cyclohexene (C6H10), cyclohexane (C6H12), styrene (C8H8), and ethylbenzene (C8H10) which allow us to examine the gradual development of delocalization of the corresponding pi electron systems. Due to the high experimental resolution, vibrational progressions can be partly resolved in the spectra. The experimental spectra are compared with theoretical NEXAFS spectra obtained from density-functional theory calculations where electronic final-state relaxation is accounted for. The comparison yields very good agreement between theoretical spectra and experimental results. In all cases, the spectra can be described by excitations to pi*- and sigma*-type final-state orbitals with valence character, while final-state orbitals of Rydberg character make only minor contributions. The lowest C 1s-->1pi* excitation energy is found to agree in the (experimental and theoretical) spectra of all molecules except for 1,3-cyclohexadiene (C6H8) where an energy smaller by about 0.6 eV is obtained. The theoretical analysis can explain this result by different binding properties of this molecule compared to the others.

Hydrogen stability in hydrogenated amorphous carbon films with polymer-like and diamond-like structure

“…This has been observed for the case of well-defined bonding environments in C 6 -ring molecules, which depending on the number of double bonds within the molecule exhibit significant variations in the XANES C-H band from increased intensity at higher energies in benzene (i.e., one H per C atom) to dominance of the band at lower energies in cyclohexane (i.e., two H per C atom). 42 When dealing with solids instead of isolated molecules, the shape of the C-H band is also sensitive to the degree of order beyond first neighbors, as has been shown for the case of polyethylene chains with different number of lateral branches. 43 In the case of our a-C:H films, the situation is even more complex, since a mixture of alkane chains and different C-ring sizes is present, and it is difficult to make a direct assignment of the observed features.…”

The role of carbon species in heterogeneous catalytic processes: an in situ soft x-ray photoelectron spectroscopy study

“…There were no distinct features in the 1s to σ* region (~290-320 eV) which would indicate the formation of a well ordered form of carbon, such as in the case of highly ordered graphite [49]. The 3.5% V/alumina and 8% V/alumina had similar K-edges, which corresponded to disordered carbon [50]. The 1% V/alumina catalyst showed however additional features on the low energy side of the main C1s to π* transition.…”

Characterization of refractory organic substances by NEXAFS using a compact X-ray source

“…However, as seen from NEXAFS spectra of small, well-understood molecules Hitchcock 1987, 1988;Sham et al 1989;Cooney and Urquhart 2004;Kolczewski et al 2006;Bâldea et al 2007;Solomon et al 2009), shifts of peak positions and absorption edges occur, depending on, e.g., the chemical environment, the substrate, or the state of aggregation. Furthermore, the functional and other subgroups in such large compositions are regarded as independent units.…”