• B N Khanna

      Articles written in Pramana – Journal of Physics

    • The infrared spectra of tutton salts 1. A comparative study of (NH4)2 M″(SO4)2·6H2O (M″=Ni, Co or Mg)

      B Singh Shashi P Gupta B N Khanna

      More Details Abstract Fulltext PDF

      The infrared spectra of (NH4)2M″(SO4)2.6H2O has been analysed in the region 4000–250 cm−1. The dynamics of each crystal has been discussed in terms of 234 phonon modes, including 3 acoustical ones, using the unit cell approximation. The ambiguity in the assignments of the bands in the region 900–500 cm−1 has been removed by assigning the bands in this region to the libratory modes of H2O molecules. It has been concluded that the NH4+ and SO42− ions have a symmetry lower thanTdand also the complex [M″(H2O)6]2+ has a symmetry lower than Oh. The hydrogen bonding is the strongest in the Ni-salt and the weakest in the Mg-salt.

    • The infrared and laser Raman spectra of K2Zn(SO4)2 · 6H2O

      B Singh Shashi Prabha Gupta B N Khanna

      More Details Abstract Fulltext PDF

      The Raman spectra of the single crystal of K2Zn(SO4)2·6H2O belonging toC2h5 space group in the 40–1200 cm−1 region in different scattering geometries and their spectra ofthe microcrystalline salt in the 1500-50 cm−1 region have been reported. The dynamics of the crystal has been described in terms of 186 phonon modes under the unit cell approximation. The weak bands in the region 400–900 cm−1 have been assigned to the libratory modes of H2O molecules in contradiction to the assignments reported by Ananthanarayanan. The ambiguities existing in the literature about the assignments ofν2c andν5c modes of [Zn(H2O)6]2+ have also been removed. The translatory and libratory modes of different units of the crystal have been identified and assignments are made using farir and Raman data on various isomorphous tutton salts.

      It has been inferred that both SO42− tetrahedron and [Zn(H2O)6]2+ octahedron undergo linear as well as angular distortions from their free state symmetries in the crystal.

    • Relationship between torsional frequency and potential barrier height forABn type molecular system

      Y S Jain B Singh B N Khanna

      More Details Abstract Fulltext PDF

      A relationship between the torsional frequency (v10) and the potential barrier (Vn) has been determined forABn type molecular system havingn-fold symmetry axis. It is found thatv10 varies prominently asVn1/2,Vn andVn2 in certain ranges. TheVn value computed fromv10 andI*r has been compared with that obtained from other experimental data for someABn units in different molecular-crystalline systems. Although there is in general a good agreement, in some cases the values differ significantly, perhaps due to the erroneous assignment of torsional mode and/or the large errors in theVn value obtained from other experimental data.

    • Libratory modes of water molecules in tutton salts

      Shashi P Gupta Y Kumar B N Khanna

      More Details Abstract Fulltext PDF

      The existence of rocking, wagging and twisting librations of different types of water molecules in tutton salts has been established from their ir spectra. These bands have been identified, following the intensity criterion of Miyazawa. The present assignments indicate that the bands due to libratory motion of H2O III in NH4Mn-, KNi-, KCo and KMn- and of H2O I in KMn- and KCu- tutton salts are out-of-plane H-bonded. The strength of the hydrogen bonding is the weakest in the (NH4)2Fe(SO4)2.6H2O.

    • Surface enhanced Raman scattering of 2-cyanopyridine adsorbed on silver colloidal particles

      Ekram Ali Shaikh Y Kumar B N Khanna

      More Details Abstract Fulltext PDF

      Surface-enhanced Raman scattering (SERS) spectra of 2-cyanopyridine (2 CP) adsorbed on silver colloidal particles have been investigated. The prominent SERS bands are observed at 556, 612, 778, 1002, 1060, 1072, 1150 and 1240 cm−1. The absolute enhancement factor of the Raman signals in SERS studies has been estimated to be of the order of 102–105 for various bands. The 2CP molecules have been ascribed to adsorb on colloidal particles in standing up fashion.

    • Inelastic light scattering in strontium borate glasses in the systemxSrO.(1−x)B2O3 and (SrCl2)y.[xSrO.(1−yx)B2O3]1−y

      M H Rahman B P Dwivedi Y Kumar B N Khanna

      More Details Abstract Fulltext PDF

      Raman spectra of strontium borate binary glasses in the systemxSrO.(1-x)B2O3 forx=0.20, 0.25, 0.30, 0.35, 0.40, and 0.50 and ternary glasses in the system (SrCl2)y.[xSrO.(1−yx)B2O3]1−y fory=0.10, 0.20, 0.30 and 0.40 andx=0.20 and 0.35, are reported. Raman spectra of the glasses show experimental evidence of glass network modifying nature of SrO in borate matrix. SrO causes a change of boron atom coordination number from 3 to 4 resulting in the complex structural groupings comprising of BO4 and BO3 units. Strontium cations are not easily accommodated in the glass structure and tend to break up the network at high concentration (x) of SrO, causing non-bridging oxygens. The effect of temperature variation of binary glasses has also been studied. The introduction of SrCl2 to the binary stronium borate glass causes a large change in intensity of low frequency Raman scattering whereas there is no change in the vibrational dynamics in the high frequency region. The temperature reduced Raman spectra represents true vibrational density of states. Martin-Brenig model developed for the low frequency region has been discussed to obtain the structural correlation range in the glass.

  • Pramana – Journal of Physics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.