Shivangi Mishra

A study of the fluorescence quenching of chlorophyll by photoacoustic spectrometry

Abstract The fluorescence quenching of chlorophyll a in acetone by chloranil, p -benzoquinone and m -dinitrobenzene has been studied using a single beam photoacoustic spectrometer. Using a modified Stern—Volmer equation the quenching constants have also been determined.

Precise Analysis of Small Wavenumber Shift of Pyridine on Dilution with H2O and D2O Using RDS Technique

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.

Raman and DFT study of polar ν(CN) and non-polar ν(C–H) modes of acetonitrile in aqueous Ag nano-colloids

Raman spectra of acetonitrile (Acn) in different millimolar (mM) concentrations adsorbed on Ag nano-colloids were recorded in the region 2100-3300cm(-1). The nu(CN) and nu(C-H) modes show blue shifts of approximately 3 and approximately 1cm(-1), respectively, when the concentration of Acn in the mixture is increased from 2 to 8mM. The blue shift of nu(CN) and nu(C-H) modes is predominantly because of adsorption of Acn molecules on Ag nano-colloids. The wave number shift and variation of intensity of the nu(CN) and nu(C-H) bands have been discussed in terms of the adsorption geometry, which probably changes from flat-on configuration at lower concentration of Acn to an end-on configuration at higher concentration of Acn. The dephasing of nu(CN) oscillator becomes considerably slower at higher concentration of Acn. The adsorption of Acn molecules on the nano-colloids was simulated using the (B3LYP) method and the basis sets used for Acn molecules and Ag atoms were 6-311++G(d,p) and Lanl2dz, respectively.