Evaluation Of Chemical Shifts Research Articles

Silicon-doping makes the B12N12 insulator to an n or p-semiconductor

Density functional theory (DFT) calculations were performed to investigate the electronic and structural properties of pristine and Si-doped B12N12 fullerene in SiB and SiN models in order to evaluate the influence of Si doping on B12N12 fullerene. The optimized structures, structural parameters, dipole moments, binding energies, energy gaps, Fermi level energies (EFL), work function (Φ), and chemical shifts have been evaluated for the pristine and two Si-doped B12N12 fullerene structures. It was found that the values of energy gap and work function of the SiB and SiN models are decreased, so that the B12N12 insulator converts to an n or p-semiconductor in the SiB and SiN models. Also, a better value of binding energy was obtained for the SiB model in comparison with the SiN model. The evaluation of chemical shifts indicated that the doped Si atom significantly influence on the chemical shifts of the B12N12 fullerene, especially in the SiN model. The doped Si atom could employ an electric field on the B and N atoms of Si-doped B12N12 structures, so that their chemical shifts go to lower fields.

Chemical shifts in X-ray and photo-electron spectroscopy: a historical review

A review with historical emphasis is given of the discovery and evaluation of chemical shifts in X-ray and photo-electron spectroscopy. The discovery and interpretation of the shifts in the X-ray spectra in the early 1920s are treated as an introduction and general background. The discovery of the shifts in photo-electron spectra, discovered in the late 1950s, and its interpretation, which led to the invention of the electron spectroscopy for chemical analysis (ESCA) method in the early 1960s, are then reviewed. Various methods of evaluating the core-electron binding energies and chemical shift are discussed—from atomic self-consistent field calculations in the early 1960s to quite sophisticated many-body and density-functional calculation in the late 1990s.

Quantitative studies of hydrogen-bonding equilibria between phenylacetylene and ethers by nuclear magnetic resonance and infrared spectroscopy: a comparison of methods

A general n.m.r. method is described for the evaluation of chemical shifts of weak 1:1 complexes and their equilibrium quotients of formation. This method takes into consideration self-association and/or magnetic anisotropy of the acidic component. It has been applied to hydrogen-bonding interactions between phenylacetylene and a series of ethers and thioethers in carbon tetrachloride solution at 33·5°. The equilibrium quotients obtained are compared with those determined by established i.r. absorption techniques. Correlations have been observed between the equilibrium quotients and the chemical shifts, molar absorptivities, and i.r. absorption band shifts of the hydrogen-bonded species.