| Abstract
| - Quantitative optical oscillator strength spectra for C 1s excitation and ionization of gas-phase biphenyl,decafluorobiphenyl, and 2,2‘-bis(bromomethyl)-1,1‘-biphenyl have been derived from electron energy lossspectroscopy recorded under electric dipole dominated conditions. The C 1s X-ray absorption spectrum ofhexaphenylbenzene has been recorded in the solid state. The C 1s spectral features are interpreted with theaid of ab initio calculations for core excitation of benzene, biphenyl, hexafluorobenzene, and decafluorobiphenyl.A weak feature at 287.7 eV in biphenyl is identified as a C 1s → π*deloc transition, characteristic of ring−ringdelocalization. Its intensity and position are shown to be related to the average torsion angle and thus theextent of π−π-interaction between adjacent aromatic rings. The effects of perfluoro substitution on coreexcitation spectra are also characterized and discussed.
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