• S K Sarkar

      Articles written in Journal of Chemical Sciences

    • Absorption and emission spectra of isomeric tolunitriles

      A Maiti S K Sarkar G S Kastha

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      Absorption and emission characteristics ofo-, m- andp-tolunitriles in polar and non-polar solvents under different conditions have been investigated in detail. Solvatochromic shifts of band origin of these molecules in non-polar solvents show that their dipolemoments in the first excited singlet state are almost the same while its value in the second excited singlet is larger in the metathan in the para-isomer. Vibronic analyses of the low temperatures absorption, fluorescence and phosphorescence spectra of all the three molecules have provided evidence that these molecules are slightly distorted in the first excited singlet state while such distortion in the phosphorescence emitting triplet state is larger. The data on fluorescence and phosphorescence quantum yield and phosphorescence lifetime of the tolunitriles are reasonably interpreted as showing that in these molecules, particularly m-andp- tolunitriles, the internal conversion rate from the first excited singlet to the ground state is probably small and that the charge transfer character of the triplet state in thep-isomer is larger than that in the meta.

    • Control strategies for laser separation of carbon isotopes

      V Parthasarathy A K Nayak S K Sarkar

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      Laser isotope separation (LIS) by infrared laser chemistry of polyatomic molecules has come a long way since its discovery. The last decade has seen considerable efforts in scaling up of the process for light elements like carbon, oxygen and silicon. These efforts aim at ways to improve both the enrichment factor and the throughput. The achievement is quite significant especially for carbon isotope separation wherein macroscopic operating scales have been realized. We report our studies on the IR laser chemistry of two promising systems, viz. neat CF2HCl and CF3Br/Cl2. We have investigated conditions for optimizing the dissociation yield and selectivity using natural samples containing l.l%C-13.Wealso highlight our current efforts for scaling up the process. These include the design aspects of a photochemical reactor with multipass refocusing Herriott optics for efficient photon utilization, development of a cryogenic distillation set up and a preparative gas chromatograph for large scale separation/collection of the isotopically enriched photoproduct in the post-irradiation stage.

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