Influence of substituents on the N K X-ray absorption near-edge structure of pyrrole derivatives

International audienceThe spectroscopy of the unoccupied molecular orbitals of gaseous pyrrole and pyrazole has been studied by electron impact under electric dipole scattering conditions (2 KeV, small angle) and the inner-shell electron energy loss method. The core-excitation spectra have been recorded at the C1s and N1s edges with 0.2 eV resolution, resolution allowing to observe separately the transitions from the carbon atoms with different chemical environment. Ab initio calculations, using the equivalent core model, were performed to help in the interpretation of the spectral features. The spectra are dominated by transitions to the π* and σ* molecular orbitals. The calculations confirm that the 3b1(π*) orbital is the lowest-energy unoccupied one in pyrrole. In several cases, the intensity of the Rydberg excitations is enhanced by an important valence σ* character of the Rydberg orbitals

Section: Nitrogen 1s Excitation Spectrumsupporting

confidence: 53%

“…We have recorded the electron energy loss spectra of pyrrole at the C1s and N1s edges with a 0.2 eV resolution which is better than in previous studies 19,26,27 and the same at both edges. We report the electron energy loss spectra of pyrazole at the C1s and N1s edges with the same 0.2 eV resolution.…”

Section: Introductionmentioning

confidence: 99%

Electronic excitation of gaseous pyrrole and pyrazole by inner-shell electron energy loss spectroscopy

Duflot

Hannay

Flament

et al. 1998

“…The second and third peaks ͑2 and 3͒ visible in all three spectra can be related to delocalized * resonances. 25,26 C. Resonant and nonresonant x-ray emission spectra at the carbon K-edge Figure 4 shows a schematic energy level diagram of the transitions involved in the x-ray processes. The x-ray emission process of PANi is governed by the 1s˜2p dipole transitions between the localized core level and the valence band.…”

Section: Resultsmentioning

confidence: 99%

The electronic structure of polyaniline and doped phases studied by soft x-ray absorption and emission spectroscopies

Magnuson

Guo

Butorin

et al. 1999

The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant soft x-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped ͑protonated͒ phases for both the carbon and nitrogen contents. The resonant x-ray emission spectra show depletion of the electron bands due to the selective excitation which enhances the effect of symmetry selection rules. The valence band structures in the x-ray emission spectra attributed to the bands show unambiguous changes of the electronic structure upon protonation. By comparing to x-ray absorption measurements, the chemical bonding and electronic configuration is characterized.

“…The ISEELS data were taken previously, and are similar to the experimental NEXAFS vapor spectra. 14,16,17 The large first feature, Feature 1, has been assigned to a nitrogen 1s 1π*(3b 1 ) feature. The second feature, Feature 2, has been variously assigned to a combination of transitions including those to the nitrogen 4p state and a variety of σ* features, including σ*(C-N) and σ*(C-H).…”

Section: Nitrogen K-edgementioning

confidence: 99%

“…13 Previous study of pyrrole has shown that its solid form has very similar NEXAFS spectra to the inner shell electron energy loss spectroscopy (ISEELS) measurements of pyrrole in the gas phase. [14][15][16][17] This implies that in the solid, the orbitals of pyrrole do not exhibit significant hybridization.…”

Section: Introductionmentioning

confidence: 99%

Auto-oligomerization and hydration of pyrrole revealed by x-ray absorption spectroscopy

Schwartz

Uejio

Duffin

et al. 2009

Near edge x-ray absorption fine structure (NEXAFS) spectra have been measured at the carbon and nitrogen K-edges of the prototypical aromatic molecule, pyrrole, both in the gas phase and when solvated in water, and compared with spectra simulated using a combination of classical molecular dynamics and first principles density functional theory in the excited state core hole approximation. The excellent agreement enabled detailed assignments. Pyrrole is highly reactive, particularly in water, and reaction products formed by the auto-oligomerization of pyrrole are identified. The solvated spectra have been measured at two different temperatures, indicating that the final states remain largely unaffected by both hydration and temperature. This is somewhat unexpected,since the nitrogen in pyrrole can donate a hydrogen bond to water.3