Rotational dynamics of propylene inside Na-Y zeolite cages

We report here the quasielastic neutron scattering (QENS) studies on the dynamics of propylene inside Na-Y zeolite using triple axis spectrometer (TAS) at Dhruva reactor, Trombay. Molecular dynamics (MD) simulations performed on the system had shown that the rotational motion involves energy larger than that involved in the translational motion. Therefore, rotational motion was not observed in our earlier QENS studies on propylene adsorbed Na-Y zeolite using a higher resolution spectrometer at Dhruva. Analysis of the TAS spectra revealed that the quasielastic broadening observed in propylene-loaded zeolite spectra is due to the rotational motion of the propylene molecules. This is consistent with our simulation result. Further, the rotational motion is found to be isotropic. The rotational diffusion coefficient has been obtained.      

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Coherent neutron inelastic scattering intensifies for two low-frequency Γ₄ internal modes in anthracene-d₁₀ have been measured at several different Brillouin zone centres. These intensifies have been used to determine the eigenvectors of the two modes involved. It is shown that the motion in both cases is a combination of a butterfly motion (B) and a twisting motion (T). The energy proportions in these two modes are 0.97B and 0.03T (±0.01) for the mode at 3.16 THz and 0.94T and 0.06B (±0.04) for the mode at 4.60 THz. This experimental result strengthens our reliance on model calculations for the assignment of phonon frequencies measured by neutron coherent inelastic scattering.     

Electrons, phonons and superconductivity in C16 structured Zr2Fe

Inelastic neutron scattering and low-temperature specific heat measurements are reported for a polycrystalline sample of Zr₂Fe. Lattice dynamical calculation of the phonon spectrum, along with first-principles LMTO electronic structure calculations have been used for deriving the specific heat parameters, the electron–phonon coupling constant and the superconducting transition temperature. The results are in fair agreement with the experimental data.     

Kinetics of the Effect of Some Bidentate Amino Acid Ligands in the Oxidation of Lactic Acid by Chromium(VI)1

The oxidation of lactic acid by Cr(VI) under acidic conditions is catalyzed by bidentate amino acid ligands such as glycine, alanine, aspartic acid and hydroxyproline. Catalysis is a function of [L]/[Cr(VI)] ratio and acidity. Pyruvic acid and acetaldehyde in a ratio of 2 : 1 are obtained as oxidation products in both uncatalyzed and catalyzed oxidation. This supports the previous understanding of the oxidation of -substituted carboxylic acids. Cromium(V) and chromium(VI) behave similarly in a C–H bond rupture (Rocek, J. and Radkowsky, A.E., J. Am. Chem. Soc., 1973, vol. 95, p. 7123), whereas Cr(IV) is responsible for C–C bond cleavage products (Wiberg, K.B. and Schafer, H., J. Am. Chem. Soc., 1969, vol. 91, p. 927).     

Search for an effect of superconductivity on the phonons in Ba(Fe1−xCox)2As2

Inelastic neutron scattering was used to search for an influence of superconductivity on the phonons in optimally doped and in slightly overdoped Ba(Fe_1?xCo_x)₂As₂, x = 0.06 and x = 0.10. The study focused on phonons with energies close to the superconducting gap energy 2Δ because it is well known that such phonons will respond most strongly to the opening of the gap. We were able to obtain high quality data but nevertheless, we could not detect any influence of superconductivity on the phonons, neither on the linewidths nor on the frequencies. Our results imply that any coupling of low energy phonons to the electrons has to be very small, much smaller than observed in conventional superconductors with a high T_c. Our results are in line with the low coupling strength predicted by density functional theory for the investigated phonon branches.     

The pressure dependence of the low-frequency Raman spectra of crystalline biphenyl and p-terphenyl

Raman spectra as a function of hydrostatic pressure are presented for crystalline biphenyl and p-terphenyl. The observed changes in the low-frequency Raman spectra of crystalline biphenyl indicate that there are probably some changes in the crystal or molecular structure with increasing pressure. The Raman spectra of p-terphenyl have no evident anomalies at pressures up to 33 kbar.     

Study of one-mode,two-mode and three-mode phonon behavior in mixed zinc blende alloys

In this paper, we put forth a microscopic interpretation of the characteristics of vibrational spectra of zinc blende semiconductor alloys arising due to either difference in masses or contrast in bond lengths. Previous Raman and infrared experiments have helped in identifying two mode vibrational behaviors in mixed systems of Zn_1−xMg_xSe and Zn_1−xMg_xTe in contrast to the one-mode behavior in Zn_1−xMg_xS. Our lattice dynamics computations have elucidated that in addition to the mass of the anion, bond length anomalies, energy separation between the two sets of optical modes, and the magnitudes of the scattering cross section play an important role in the observance of one mode behavior in the S system, two mode behavior for the whole of the composition range in the Se and Te systems, and an additional Be–Te like vibrational doublet in case of Zn_1−xBe_xTe. Our calculations incorporate the treatment of disorder through a supercell approach. The calculated lattice constants for different concentrations, the bimodal bond length distribution, as well as the phonon frequencies at the Brillouin zone centre are in good agreement with the available experimental data.