Isomeric sensitivity of the C 1s spectra of xylenes

Abstract

Oscillator strengths for C 1s inner-shell excitation of the isomeric xylenes (ortho-, meta-and para-) have been derived from electron energy loss spectra recorded under scattering conditions dominated by electric dipole transitions. The lineshape of the C 1s → p* transition is found to be dependent on the substitution pattern, with para-xylene exhibiting two components, orthoxylene a single asymmetric peak, and meta-xylene a single symmetric peak at an instrumental resolution of 0.35 eV. Improved virtual orbital ab initio calculations were carried out on all three species, providing spectral shapes in reasonable agreement with experiment. The calculations indicate that the transition responsible for the splitting which is observed only in the C 1s spectrum of para-xylene is associated with the methyl-substituted ring carbons, for which there is a somewhat larger chemical shift in the para relative to the ortho-or meta-isomers. These results are compared to other recent studies of C 1s spectroscopy of di-substituted benzenes (dimethylphthalates and nitroanilines) in order to investigate trends in the sensitivity of C 1s spectroscopy to isomeric substitution patterns. ᭧

Elastic electron scattering from ortho-, meta-, and paraxylenes, C8H10

“…They found all three isomers were essentially identical with only minor differences. Inner shell excitation of the C 1s orbital was made by Eustatiu et al [16], who observed very similar spectra for all three isomers. Similar observations for the total ionization cross section of the isomers of xylene was made by Jiao and…”

Chemical Trends in the Near-Edge X-ray Absorption Fine Structure of Monosubstituted and Para-Bisubstituted Benzenes

“…The calculated excitation energies, ionization potentials, term values, and oscillator strengths are listed in Table . There is a large body of previous computational work for many of these species, including ab initio IVO calculations of dimethyl terephthalate, N -phenylcarbamic ethyl ester, N , N ‘-diphenyl urea, and p -xylene, as well as extended Hückel MO calculations of benzaldehyde, benzoic acid ethyl ester, terephthaldehyde, benzene-1,4-diol, and phenol . We have repeated these calculations here with a common basis set to permit a systematic comparison of experiment to theory.…”

Near-Edge X-ray Absorption Fine Structure Spectroscopy of MDI and TDI Polyurethane Polymers

“…In the MDI polymers, each phenyl ring is bonded to one amide group and one methylene group; while in the TDI polymer, each phenyl ring is bonded to two amide groups and one methyl group. The C 1s spectra of xylenes demonstrate that the C−R shift due to methyl substitution is very small (∼0.1 eV) . Therefore, the methylene C−R shift can be neglected and only the amide C−R shifts are significant.…”

“…The C 1s spectra of xylenes demonstrate that the C-R shift due to methyl substitution is very small (∼0.1 eV). 21 Therefore, the methylene C-R shift can be neglected and only the amide C-R shifts are significant. In MDI-based polymers, one phenyl carbon will have the C-R shift and five phenyl carbons will not; in the TDI-based polymers, two phenyl carbons will have the C-R shift while four carbons will not.…”