Concentration Dependence Of Linewidths Research Articles

Structural disorder and optical properties of congruent lithium niobate crystals doped with zink and boron

From the concentration dependence of the widths and intensities of Raman lines and from the patterns of photoinduced light scattering, it is found that the mechanism of incorporation of Zn2+ cations into the LiNbO3 crystal structure changes with increasing concentration of zinc in the melt, which leads to an abrupt anisotropic expansion of oxygen octahedra along the polar axis. In this case, the number of kinks in the concentration dependence of linewidths (5) considerably exceeds the number of concentration threshold (2) known from the literature. It is shown that B3+ ions almost do not enter the cationic sublattice of the LiNbO3 crystal but changes the melt structure, so that the LiNbO3:B crystal is characterized by a high structural and optical homogeneity and a low photorefractive effect.

Study of vibrational dephasing of CCl stretching mode of 2Cl‐pyridine and 3Cl‐pyridine in methanol environment by polarized Raman study and DFT calculations

AbstractRaman spectra of [2Cl‐pyridine (2Cl‐p) + methanol] and [3Cl‐pyridine (3Cl‐p) + methanol] mixtures were recorded in the region 360–480 cm−1 and the concentration dependence of linewidths and peak positions of the isotropic part of the Raman scattered radiation for the CCl stretching mode were studied in the light of the existing models. The analysis of the results revealed that concentration fluctuation and diffusion simultaneously play a role in the dephasing of the CCl stretching mode. The optimized structures of the reference systems, 2Cl‐p and 3‐Cl‐p, and their various complexes with methanol were calculated by density functional theory (DFT) geometry optimization technique using B3LYP functional and 6–31 + G(d,p) basis set. On the basis of the results of geometry optimization and energy minimization calculation, we propose that the complex formed as a result of hydrogen bonding of one 3Cl‐p molecule with three methanol molecules is more stable than the one formed by one 3Cl‐p molecule and two methanol molecules. This study presents an explanation of changes in spectral features of ortho/meta Cl‐substituted pyridines supported by DFT derived optimized geometries. Equilibrium constants have been obtained from the spectral data for one of the systems (2Cl‐pyridine + methanol). Copyright © 2006 John Wiley & Sons, Ltd.

Hydrogen-Bonded Pyridine−Water Complexes Studied by Density Functional Theory and Raman Spectroscopy

Density functional theory (DFT) at the B3LYP/6-31++G(d,p) level was employed to obtain the optimized geometries and vibrational spectra of several pyridine(Py)−water(W) complexes with stoichiometric ratios ranging from 2:1 (Py2W) to 1:3 (PyW3). The harmonic vibrational wavenumbers of pyridine ring modes and the fundamental modes of water were calculated in order to examine the influence of hydrogen bonding on the normal modes of both pyridine and water upon complexation. The Raman spectra in the wavenumber region 960−1060 cm-1 covering the ring modes ν1 and ν12 of pyridine (in Wilson's notation) as a function of pyridine mole fraction were recorded. The integrated Raman intensities in the isotropic components of the spectra were used to determine the relative concentration of “free” pyridine molecules in close neighborhood with other Py−W complexes. The combination of both experimental wavenumbers yielding the overall shift induced by the entirety of hydrogen-bonded complexes in the mixture and the DFT-derived vibrational wavenumbers of the isolated species provides the possibility to probe concentration profiles as a function of pyridine mole fraction. The examination of the concentration dependence of line widths reveals that the counter competing influences of different dynamic processes are simultaneously present in this binary mixture.

ESR spectra of powdered samples of copper(II)-doped bis(diethyldithiocarbamato)nickel(II)—Concentration dependence of linewidths

Room-temperature X-band electron spin resonance spectra of copper(II)-doped nickel diethyldithiocarbamate powders have been studied as a function of copper(II) doping. At low dopant concentrations (less than 5 mole %) the concentration variation of linewidths predicted by a simple dipolar broadening formulation is in good agreement with experiment. At higher dopant concentrations the observed spectra indicate the presence of substantial number of large copper(II) diethyldithiocarbamate clusters in the samples examined.