• T N Misra

      Articles written in Journal of Chemical Sciences

    • Effect of adsorption of vapours on the electrical conductivity of some polyene semiconductors: adsorption and desorption kinetics

      Alpana Ghosh Biswanath Mallik T N Misra

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      The change in semiconductive properties of β-apo-8′-carotenal, astacene and methyl bixin on adsorption of various vapours on the crystallite surfaces has been studied at a constant sample temperature. The adsorption of vapours enhances the semiconductivity of the polyenes appreciably. This enhancement depends on the chemical nature and also on the pressure of the adsorbed vapour. The adsorption and desorption kinetics follow the modified Roginsky-Zeldovich relation. A two stage desorption process, the first stage of which gives a Lennard-Jones potential energy curve and is followed by a rate-determining transition over a potential energy barrier to the second stage of adsorption forming weakly bound complexes between the vapour molecules and the polyene crystallites, can explain satisfactorily the experimentally observed kinetic data.

    • Effect of adsorption of vapours on the electrical conductivity of a series of pyrenyl polyenes: adsorption and desorption kinetics

      A Sircar T N Misra

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      This paper deals with the change in electrical conductivity in a series of pyrenyl polyenes of the typeR-(CH=CH)n-R (whereR stands for the pyrenyl group andn=1−4) on adsorption of various vapours. Appreciable change in the conductivity is observed. The adsorption and desorption kinetics follow a modified Roginsky-Zeldovitch equation. The results show that in all these vapour-semiconductor systems, adsorption is a two-stage process.

    • A multistage adsorption process in 15–15′cis β-carotene crystal: Electrical conductivity enhancement on chemical vapour adsorption

      Bani Mitra T N Misra

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      The phenomenon of conductivity enhancement on adsorption of various chemical vapours has been used as a probe to study the adsorption and desorption process in 15–15′cis-β-carotene crystals. The kinetics follow a modified Roginsky-Zeldovich equation. From the analyses of the kinetics, the adsorption has been found to be multistage at higher vapour pressure. An additional physisorption stage shows up in the initial stage of the well-known three stage adsorption process. Measures of activation energies of adsorption and desorption at different stages have been estimated.

    • Photoconductive properties of zeaxanthin in a sandwich cell

      Dilip Ghosh Prabir Pal T N Misra

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      Photoconduction decay in zeaxanthin in a sandwich cell has been measured as a function of applied field and temperature in longer time domains (5–35s). The results show that the gap states decrease exponentially with characteristic temperatureTc≈450 K at an applied field of 1·77×103 V/cm. When the sample temperature is 293 K,Tc is found to be voltage-dependent and follows the empirical relationTc≈A exp (−bV). The field effect onTc is suggested to arise from the field effect on trapping rate. Light intensity dependence of photocurrent satisfies the power lawIph∞IBγ with γ varying between 0–61 and 0–58 depending on the applied voltage at low excitation light intensity. At high intensities γ=1·2.Tc values evaluated from decay and light intensity dependence measurements show excellent correlation.

    • Laser Raman spectroscopic study of photoreaction dynamics inp-chloro cinnamic acid crystal

      Subhasis Chakrabarti M Gantait T N Misra

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      Raman phonon spectroscopy has been used to study photodimerization reaction inp-chloro cinnamic acid (pCCA) crystal. The β-form of the crystal yields the 4,4′-dichloro-β-truxinic acid dimer. Six distinct low frequency phonon bands are observed in thepCCA monomer crystal. On reaction progress, these bands show a monotonic shift to lower frequencies and broaden out. Finally, in the dimer crystal the phonon spectrum shows two weak broad bands. These results suggest that the reaction is homogeneous in the initial stages and, as the product concentration increases, the lattice becomes highly disordered. The reactant and the product were characterised by infrared and Raman spectroscopy. The disappearance of aliphatic C=C bond stretching vibration and appearance of cyclobutane ring deformation and cyclobutane ring-breathing vibrations on reaction confirm photodimerization by cyclobutane ring formation. The large Stoke's shift between the absorption and emission band suggest strong exciton-phonon coupling in the monomer lattice. This reaction seems to be phonon-mediated.

    • Spectroscopic study of photoreaction dynamics inp-bromo cinnamic acid

      Manash Ghosh A K Maity Subhasis Chakrabarti T N Misra

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      The photodimerization reaction inp-bromocinnamic acid (p-BCA) in the crystalline state has been probed by Raman phonon spectroscopy. Monotonic redshift of the phonon bands and nonappearance of any new phonon bands on reaction progress suggest that the reaction is homogeneous and the reactant and the product form a solid solution. It is further observed that a low frequency phonon at 18·6 cm−1 softens on photoexcitation and progress of reaction. The photoreaction inp-BCA crystal therefore seems to be mediated by the lattice phonon. In the IR spectrum disappearance of the aliphatic > C=C < stretching frequency and appearance of cyclobutane ring deformation and ring stretching modes on reaction confirm photodimerization by cyclobutane ring formation. Considerable overlap between the absorption and emission bands shows that the exciton-phonon coupling is not very strong in the monomer crystal.

    • Raman spectral study of vibrational relaxation in acetophenone

      D Bhattacharjee A Purkayastha T N Misra

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      The isotropic Raman band of the C=O stretching mode of the acetophenone molecule has been recorded in a number of solvents of varying physicochemical properties. The experimental results suggest that dispersion forces are responsible for the observed isotropic frequency shift. The variation in the band shape parameters has been studied as a function of the hydrodynamic properties of the solvents. The effect of solvent viscosity on linewidth (Γiso) has been studied in detail. The concept of microviscosity is shown to account for the bandwidth of the isotropic component of the Raman band.

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