• Volume 1, Issue 6

      December 1973,   pages  243-287

    • The fractional ionic character of alkali and silver halide crystals

      Jai Shanker M P Verma

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      The fractional ionic character of alkali and silver halide crystals is defined in terms of the deviations from the additivity rule for polarizabilities of ions. The electronic polarizabilities of ions are calculated using an empirical relationship according to which the electronic polarizability of an ion can be assumed to be directly proportional to the cube of its radius. The calculated ionicities indicate that the alkali halides are nearly or more than 90% ionic and silver halides are much less ionic which is also evident from the Phillips ionicity scale.

    • Structure determination of Ls-threonine by neutron diffraction

      M Ramanadham S K Sikka R Chidambaram

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      The structure of the aminoacid, Ls-threonine [NH3+ CH(CHOHCH3)COO], space groupP212121,a=13.630(5),b=7.753(1),c=5.162(2) Å,z=4, has been determined from neutron diffraction data using direct methods. The intensities of 1148 neutron Bragg reflections were measured from a single crystal. The structural parameters were refined by the method of least squares using anisotropic temperature factors. The finalR(F2) is 0.068. The structure was also refined from the x-ray data of Shoemakeret al (1950J. Am. Chem. Soc.72 2328); there is good agreement between the two sets of heavy atom parameters. The parameters of hydrogen atoms are of course more precisely determined in our neutron study. The molecular conformation and the hydrogen bonding scheme are discussed. Weighted average values of bond distances and angles from 14 aminoacid structures with ionized carboxylic groups studied by neutron diffraction at Brookheven and Trombay are also presented.

    • Coexistence curve and rectilinear diameter in the critical liquid system carbon disulphide+nitromethane

      E S R Gopal R Ramachandra P Chandra Sekhar

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      The phase boundary of the binary liquid system CS2+CH3NO2 is studied over nearly six decades in reduced temperature 3×10−6<ε=(TCT)/TC<2×10−1 and over the composition range 8-98 mole % of CS2. The critical parameters areTC=335.132K andxC=57.34 mole % of CS2. A single critical exponentβ=0.315±0.004 fits the observations over the entire range with no indication ofβ increasing to the classical value of 1/2 far away fromTC. The diameter of the coexistence curve shows a rectilinear behaviour only far away fromTC. NearTC, the deviation ΔX from the rectilinear law seems to fit a curve of the form ΔX=fε7/8 exp (−h), the derivative of which has a singularity like that of specific heat. An ambiguity in the analysis of the data in terms of mole fractions and volume fractions is pointed out. It is also suggested that the curvature of the diameter may be much weaker in a liquid-gas system and hence might have escaped detection.

    • Shape-excited states of28Si

      D R Kulkarni S P Pandya

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      The Hartree-Fock (HF) minima for the nucleus28Si were obtained for the prolate, oblate and spherical shapes using the interaction obtained by Preedom and Wildenthal. The interaction gives rise to large energy separation between the prolate and the oblate shapes. The spherical solution is just 2 MeV above the lowest HF (oblate) minimum. The spectrum projected from the oblate HF state is in good agreement with the experimental spectrum. The transition probabilities for the different energy levels also agree reasonably well. The configuration mixing calculations performed on the basis of states projected from the three shapes indicate that there is no significant mixing of different projected states. The second 02+ state, thus obtained, corresponds to the third 03+ state in the experimental spectrum and stems dominantly from the spherical HF state. It is seen that the structure of the energy levels of28Si, especially the second 02+ level is very sensitive to the two body interaction. The results are compared with those obtained using the renormalised interaction of Kuo.

    • Double hypernuclei and the ΛΛ interaction

      G Bhamathi K Prema Indumathi Seshadri

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      The double hypernuclei$$ \wedge \wedge He^6 $$ and$$ \wedge \wedge Be^{10} $$ have been analysed using purely attractive nonlocal separable potential. These double hypernuclei have been considered as three body (Λ+Λ+α) and four body (Λ+Λ+α+α) systems respectively. A consistent description of both the systems has been obtained for an intrinsic rangeb=1.5 fm of the ΛΛ interaction in the1S0 state. For the purely attractive Yukawa potential this corresponds to the two pion exchange range. The strength of the ΛΛ interaction deduced from the double hypernuclei was found insufficient to bind the two body ΛΛ system. The lightest double hypernucleus that is expected to be bound is$$ \wedge \wedge He^5 $$. The heavier double hypernuclei$$ \wedge \wedge C^{14} $$ and$$ \wedge \wedge O^{18} $$ have also been analysed. The binding energies obtained are in reasonable agreement with those of earlier workers.

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