Showing papers by "Ranjan K. Singh published in 2011"
TL;DR: In this article, the hydrogen bonding between pyrimidine and methanol (M) as H-donor was investigated for binary mixtures of Pd and M at 28 different mole fractions and the results of density functional theory calculations on structures and vibrational spectra of neat pd and eight Pd/M complexes were obtained.
Abstract: We report on the hydrogen bonding between pyrimidine (Pd) and methanol (M) as H-donor in this study. Hydrogen bonds between pyrimidine and methanol molecules as well as those between different methanol molecules significantly influence the spectral features at high dilution. The ring-breathing mode ν1 of the reference system Pd was chosen as a marker band to probe the degree of hydrogen bonding. Polarized Raman spectra in the region 970–1020 cm−1 for binary mixtures of (pyrimidine + methanol) at 28 different mole fractions were recorded. A Raman line shape analysis of the isotropic Raman line profiles at all concentrations revealed three distinct spectral components at mole fractions of Pd below 0.75. The three components are attributed to three distinct groups of species: ‘free Pd’ (pd), ‘Pd with low methanol content’ (pd1) and ‘Pd with high-methanol content’ (pd2). The two latter species differ considerably in the pattern and the strengths of the hydrogen bonds. The results of density functional theory calculations on structures and vibrational spectra of neat Pd and eight Pd/M complexes with varying methanol content support our interpretations of the experimental results. A nice spectra–structure correlation for the different cluster subgroups was obtained, similar to earlier results obtained for Pd and water. Apart from N···H and O···H hydrogen bonds between pyrimidine and methanol, O···H hydrogen bonds formed among the methanol molecules in the cluster at high methanol content also play a crucial role in the interpretation of the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.
27 citations
TL;DR: In this article, the Raman spectra of neat propionaldehyde [CH3CH2CHO or propanal (Pr)] and its binary mixtures with hydrogen-donor solvents, water (W) and methanol (M), with different mole fractions of the reference system, varying from 0.1 to 0.9 at a regular interval of 0.
Abstract: The Raman spectra of neat propionaldehyde [CH3CH2CHO or propanal (Pr)] and its binary mixtures with hydrogen-donor solvents, water (W) and methanol (M), [CH3CH2CHO + H2O] and CH3CH2CHO + CH3OH] with different mole fractions of the reference system, Pr varying from 0.1 to 0.9 at a regular interval of 0.1, were recorded in the ν(CO) stretching region, 1600–1800 cm−1. The isotropic parts of the Raman spectra were analyzed for both the cases. The wavenumber positions and line widths of the component bands were determined by a rigorous line-shape analysis, and the peaks corresponding to self-associated and hydrogen-bonded species were identified. Raman peak at ∼1721 cm−1 in neat Pr, which has been attributed to the self-associated species, downshifts slightly (∼1 cm−1) in going from mole fraction 0.9 to 0.6 in (Pr + W) binary mixture, but on further dilution it shows a sudden downshift of ∼7 cm−1. This has been attributed to the low solubility of Pr in W (∼30%), which does not permit a hydrogen-bonded network to form at higher concentrations of Pr. A significant decrease in the intensity of this peak in the Raman spectra of Pr in a nonpolar solvent, n-heptane, at high dilution (C = 0.05) further confirms that this peak corresponds to the self-associated species. In case of the (Pr + M) binary mixture, however, the spectral changes with concentration show a rather regular trend and no special features were observed. Copyright © 2010 John Wiley & Sons, Ltd.
22 citations
TL;DR: In this article, the effects of chemical vapours on the Raman and infrared absorption spectra of α crystalline nickel phthalocyanine thin films were investigated and density functional theory (DFT) calculations were carried out to determine the probable geometric structures of the complexes of the vapour and phthalohyanine molecules.
22 citations
TL;DR: In this paper, a density functional theoretic (DFT) calculation on optimized geometries and vibrational frequencies of two conformers of neat (C 2 H 5 ) 2 C O in C 2 ad C 2v forms and the complexes with one and two CH 3 OH molecules with both the conformers was performed.
5 citations
TL;DR: In this article, the Raman spectra of the C-H stretching bands of three diazines; pyrimidine, pyridazine, and pyrazine were measured to analyze the wavenumber shifts experimentally.
Abstract: Abstract Diazines form various types of hydrogen bonds with water, wherein C–H groups are sometimes involved directly and sometimes indirectly. On hydrogen bond formation, the wavenumber of C–H stretching vibration are usually red shifted (normal hydrogen bond) but blue shift of C–H modes (anomalous hydrogen bond) is also possible in some cases. The Raman spectra of the C–H stretching bands of three diazines; pyrimidine, pyridazine, and pyrazine in pure form and at many concentrations in mole fractions of diazines in the mixture of diazines + water have been measured to analyze the wavenumber shifts experimentally. Theoretical wavenumber shifts have been calculated and NBO analysis has been performed using DFT methods to understand the cause of the shifts. All the four C–H stretching bands of diazines are blue shifted on dilution with water both experimentally and theoretically. The NBO calculations reveal that the cause of the shift is decrease in the charge density in the antibonding orbital of C–H bond on complex formation.
3 citations
TL;DR: In this article, the wavenumber difference of ring breathing, ring deformation and C-H stretching modes of pyridine (Py) dissolved in both H2O and D2O at equal mole fractions of the solute (Py), and the solvent (H2O/D2O) was determined precisely by using the technique of Raman difference spectroscopy (RDS).
Abstract: Abstract The wavenumber difference (Δν) of the ring breathing mode (ν1), ring deformation mode (ν12) and C–H stretching mode (ν3) of pyridine (Py) dissolved in both H2O and D2O at equal mole fractions of the solute (Py) and the solvent (H2O/D2O) has been determined precisely by using the technique of Raman difference spectroscopy (RDS) in order to analyze the relative shift caused by these two solvents. The spectra of the two systems, for which the difference spectrum is to be generated, were recorded simultaneously and the wavenumber shifts up to almost one hundredth part of the linewidth of a band could be determined precisely. The values of Δν for the three modes as a function of mole fraction are compared with the Δν obtained by the solvation of Py molecule in the media of dielectric constants equal to that of the mixture of Py and H2O/D2O at the experimental mole fractions using DFT and MP2 methods. The variation in Δν with mole fraction seems to be the result of difference of dielectric constants of Py+H2O and Py+D2O at equal mole fraction. The absolute peak position and linewidth of the three modes as a function of mole fraction have been discussed in terms of relevant models, which show the effective role of diffusion and concentration fluctuation in the mixture.
1 citations