Influence Of Anomalous Dispersion Research Articles

Aspherical-atom modeling of coordination compounds by single-crystal X-ray diffraction allows the correct metal atom to be identified.

Single-crystal X-ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid-state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical-atom least-squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld-atom refinement (Acta Crystallogr. Sect. A- 2008, 64, 383-393; IUCrJ. 2014, 1,61-79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B- 2013, 69, 91-104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear-coordinate 3d metal complexes, for which the wrong element is found if standard independent-atom model scattering factors are relied upon, are studied, and it is shown that only aspherical-atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed.

Parametric X Rays in the Region of Anomalous Dispersion

The influence of anomalous dispersion on the intensity of parametric x rays (PXR) is experimentally investigated in the present work. An experiment conducted with an inner electron beam generated by the Tomsk synchrotron with energy E 0 = 900 MeV is discussed. A Ge monocrystal 0.17 mm thick oriented so that Bragg's angle ΘB between the electron momentum direction and the (111) plane is 9°30′ is used as a target. The experimental data are compared with the results of calculations in the context of the kinematic PXR theory.

Infrared spectra of cesium chloride aqueous solutions

The aqueous solutions of CsCl were studied at room temperature by infrared (IR) spectroscopy in the entire solubility range, 0–1200 g/L, using attenuated total reflection (ATR) sampling. The influence of anomalous dispersion on the IR–ATR spectra was evaluated by calculating the imaginary refractive index, k(ν), of each sample. Factor analysis (FA) was used to determine the number and abundance of species in the solutions. FA applied to both k(ν) spectra and IR-ATR spectra produced two principal spectra with a similar abundance of species. This result indicates that, even at high salt concentration, the optical effects do not influence the chemical analysis of IR–ATR spectra. The spectral modifications related to the salt concentrations are mainly first order. Second order effects were observed, but being weak, were not investigated. The two principal spectra are related to the two species present in the solution: pure water and CsCl–solvated water. From the latter, 2.8±0.4 water molecules were calculated to be associated with each close-bound Cs+/Cl− ion pair. In the case of KCl and NaCl aqueous solutions, both of which showed the same number of species, the number of water molecules associated to an ion pair was 5.0±0.4. That the latter number is different from that of CsCl indicates that the interaction between water molecules and ion pairs is different when cation Na or K in the chloride salt is replaced by Cs.

Influence of Anomalous Dispersion on the ATR Spectra of Aqueous Solutions

Transmission spectra of aqueous solutions are difficult to obtain because in the 3 μm infrared region, the high absorptivity of water requires the use of thin films. In contrast, attenuated total reflectance (ATR) spectra of aqueous solutions, not requiring thin films, are easily obtained. Unfortunately, compared to measurements made by transmission, ATR measurements cause some variation in the band shape due to the anomalous dispersion (AD) effect. To evaluate these variations, we studied pure water and KCl aqueous solutions. We then compared the ATR spectra of both substances with the real and imaginary refractive index spectra calculated by using the Kramers–Krönig relation. As long as the proper material is used in the ATR cell and the concentration of water is not significantly decreased, then the IR-ATR measurements directly reflect the chemistry of the sample.

Influence of anomalous dispersion on the amplitude-detuning characteristic of a CO2 laser with harmonic modulation of losses

Influence of anomalous dispersion on the amplitude-detuning characteristic of a CO2 laser with harmonic modulation of losses