Near-Edge X-ray Absorption Spectra of Carbon-Nitride Molecules and Solids

Plashkevych, Oleksandr; Snis, Anders; Yang, Li; Ågren, Hans; Matar, Samir F.

doi:10.1088/0031-8949/63/1/010

Cited by 18 publications

(9 citation statements)

References 64 publications

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“…So far most of the studies of these molecules have been performed in the condensed phase. Along this line, we find a study by Plashkevych et al 3 where they calculated the NEXAFS spectra for different carbon-nitrogen molecules, clusters, and solids. The molecular and cluster spectra were calculated with the ab initio technique, while the solid state calculations were performed with the density functional full potential augmented plane wave method.…”

Section: Introductionsupporting

confidence: 72%

The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase

Vall-llosera¹,

Gao²,

Kivimäki³

et al. 2008

The Journal of Chemical Physics

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Near edge x-ray absorption fine structure spectra have been measured and interpreted by means of density functional theory for five different azabenzenes (pyridine, pyridazine, pyrimidine, pyrazine, and s-triazine) in the gas phase. The experimental and theoretical spectra at the N 1s and C 1s edges show a strong resonance assigned to the transition of the 1s electron in the respective N or C atoms to the lowest unoccupied molecular orbital with pi(*) symmetry. As opposed to the N 1s edge, at the C 1s edge this resonance is split due to the different environments of the core hole atom in the molecule. The shift in atomic core-level energy due to a specific chemical environment is explained with the higher electronegativity of the N atom compared to the C atom. The remaining resonances below the ionization potential (IP) are assigned to sigma or pi [corrected] orbitals with mixed valence/Rydberg [corrected] character. Upon N addition, a reduction of intensity is observed in the Rydberg region at both edges as compared to the intensity in the continuum. Above the IP one or more resonances are seen and ascribed here to transitions to sigma(*) orbitals. Calculating the experimental and theoretical Delta(pi) term values at both edges, we observe that they are almost the same within +/-1 eV as expected for isoelectronic bonded pairs. The term values of the pi(*) and sigma(*) resonances are discussed in terms of the total Z number of the atoms participating in the bond.

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Section: Introductionsupporting

confidence: 72%

The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase

Vall-llosera¹,

Gao²,

Kivimäki³

et al. 2008

The Journal of Chemical Physics

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“…This leads to a single peak at the N 1s edge, for example in acetonitrile 52 and polyacrylonitrile. 53 Figure 6(c), the liquid crystal 8CB (π * peaks at 399.1 and 399.9 eV): An energy splitting can be induced in the two degenerate C ≡N π * orbitals by breaking the symme- try between x and y. This can be achieved by coupling to an anisotropic ligand, such as a π -system consisting exclusively of p x orbitals.…”

Section: Consideration Of Other Models Via Reference Compoundsmentioning

confidence: 99%

“…This can be achieved by coupling to an anisotropic ligand, such as a π -system consisting exclusively of p x orbitals. Examples are acrylonitrile, 54 benzonitrile, 55 9cyanoanthracene, 53 and 5CB. 56,57 Our N 1s spectrum of 8CB shows the characteristic doublet of low-lying π * peaks observed in all these nitriles.…”

Section: Consideration Of Other Models Via Reference Compoundsmentioning

confidence: 99%

Universal mechanism for breaking amide bonds by ionizing radiation

Johnson

Cook

Liu

et al. 2011

The Journal of Chemical Physics

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The photodissociation of the amide bond by UV light and soft x-rays is investigated by x-ray absorption spectroscopy at the C, N, and O 1s edges. Irradiation leaves a clear and universal signature for a wide variety of amides, ranging from oligopeptides to large proteins and synthetic polyamides, such as nylon. As the π∗ peak of the amide bond shrinks, two new π∗ peaks appear at the N 1s edge with a characteristic splitting of 1.1 eV. An additional characteristic is the overall intensity reduction of both the π∗ and σ∗ features at the O 1s edge, which indicates loss of oxygen. The spectroscopic results are consistent with the release of the O atom from the amide bond, followed by the migration of the H atom from the N to one of its two C neighbors. Migration to the carbonyl C leads to an imine, and migration to the C(α) of the amino acid residue leads to a nitrile. Imine and nitrile produce the two characteristic π∗ transitions at the N 1s edge. A variety of other models is considered and tested against the N 1s spectra of reference compounds.

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“…In order to reach the right stoichiometry one carbon has been added in the middle of the second cell, while the four nitrogen atoms, constituting the ''nitrogen hole,'' have been substituted with four carbons. 61 This phase is here called ␣-C 11 N 4 ͑Fig. 4͒.…”

Section: A the Graphitic And Pseudocubic C 3 Nmentioning

confidence: 99%

Density-functional theory investigation of hardness, stability, and electron-energy-loss spectra of carbon nitrides withC11N4stoichiometry

2002

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The characterization of carbon nitride films with stoichiometry C 3 N 4 is heavily restricted by the problem of getting pure crystalline samples with the right C/N ratio. However, thin films with lower nitrogen concentration ͑5-25 %͒ have been found relatively easier to deposit, for example, with reactive magnetron sputtering. It is also in this range of nitrogen content that the recently discovered ''graphiticlike → fullerenelike'' phase transition has been suggested to take place. Therefore, in order to add more information to the above experimental evidence, it is important to use theoretical methods to obtain further characterization of carbon nitride models with a high C/N ratio such as that of C 11 N 4 . It is relevant to propose a cross checking on the role played by the nitrogen concentration in determining the stability, hardness, and electronic properties of CN x compounds with different stoichiometries. For the sake of simplicity we have here compared the C 3 N 4 and C 11 N 4 systems, which are isoelectronic to each other. For this purpose two C 11 N 4 phases, namely, ␣ and ␤, are presented and investigated with density-functional-theory methods within the local density approximation. These phases contain less than ϳ30% of nitrogen than the well-known C 3 N 4 and are formally derived from the so-called pseudocubic C 3 N 4 . Cohesive properties, heats of formation, bulk and elastic moduli have been calculated and a full detailed analysis of the density-of-states and energy-loss-near-edge-structure spectra is presented. We propose that the lowering of the nitrogen concentration does not prevent the finding of new ultrahard materials and indeed brings a significant increase in the cohesive energy of carbon nitrides. However, the computed enthalpies of formation have shown values that are positive and generally larger than the analog carbon-deficient phases.

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Near-Edge X-ray Absorption Spectra of Carbon-Nitride Molecules and Solids

Cited by 18 publications

References 64 publications

The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase

The C 1s and N 1s near edge x-ray absorption fine structure spectra of five azabenzenes in the gas phase

Universal mechanism for breaking amide bonds by ionizing radiation

Density-functional theory investigation of hardness, stability, and electron-energy-loss spectra of carbon nitrides withC11N4stoichiometry

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