Showing papers by "Ranjan K. Singh published in 2006"

A new approach to explain concentration-dependent changes of isotropic Raman line width in the associated binary mixtures.

Abstract: We report on a new empirical relationship to explain the concentration-dependent isotropic Raman line width changes of a vibrational mode in uniform binary mixtures. The factors contributing to the intrinsic line width and several other broadening mechanisms are, in general, concentration-dependent. Concentration fluctuation in a microscopic volume and microviscosity are the two factors that are known to cause a concentration-dependent line width variation. These two factors combined in a specific manner successfully explain the variation of the line width with concentration strongly associated with binary systems. A readily usable empirical relationship for line width is suggested. It has been demonstrated that it can successfully explain the line width variation with concentration in a given class of hydrogen-bonded systems taking some representative binary mixtures.

Probing self-associated structures of the solute molecule, acrylonitrile, the solvent molecule 2Cl-phenol and their binary complexes via concentration-dependent Raman study and DFT calculation

Abstract: Raman study of CN-stretching mode of acrylonitrile and ring-breathing mode of 2Cl-phenol was made in the binary mixture of (acrylonitrile + 2Cl-phenol) at different molar ratios of the two components. Raman spectra were recorded in the different spectral regions, 990–1070 cm−1 and 2170–2300 cm−1. Ring-breathing mode of 2Cl-phenol exhibited two components, which were attributed to the neat and self-associated dimer of 2Cl-phenol molecules. The self-associated structure of the dimer was obtained by geometry optimization. Other structures, which were calculated, include self-associated structure of acrylonitrile and the hydrogen-bonded complex of (acrylonitrile + 2Cl-phenol). All the geometry optimizations were made using density functional theory (DFT) and B3LYP functional employing the 6–31 + G(d,p) basis set. The variations of the linewidth and the peak position with concentration are explained on the basis of a model, which includes both the effect of concentration fluctuation in a microscopic volume and the influence of concentration-dependent microviscosity based on a model proposed recently by our group. Copyright © 2006 John Wiley & Sons, Ltd.

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

Abstract: Raman 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 CCl 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 CCl 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.