• Bhupesh Kumar Mishra

      Articles written in Journal of Chemical Sciences

    • Computational study on decomposition kinetics of CH3CFClO radical

      Hari Ji Singh Bhupesh Kumar Mishra

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      The present study deals with the decomposition of haloalkoxy radical (CH3CFClO) formed from 1,1-dichloro-1-fluoroethane (HCFC-141b) in the atmosphere. The sudy is performed using ab-initio quantum mechanical methods. Out of the three plausible pathways of decomposition of the titled species, the one that involved the C-C bond scission and the other occurring via Cl-atom elimination have been considered for detailed study. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at MP2 level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2(MP2) level of theory. The path involving the Cl-elimination is found to be dominant and found to occur with a barrier height of 3.6 kcal mol-1 whereas the C-C bond scission path proceeds with a barrier of 10.0 kcal mol-1. The thermal rate constants for the above two decomposition pathways are evaluated using Canonical Transition State Theory (CTST) and these are found to be $2.9 \times 10^8 s^{−1}$ and $4.3 \times 10^5 s^{−1}$ for Cl-elimination and C-C bond scission respectively at 298 K and 1 atm. pressure. The existence of transition states on the corresponding potential energy surface is ascertained by the occurrence of only one imaginary frequency obtained during the frequency calculation. The Intrinsic Reaction Coordinate (IRC) calculation has also been performed to confirm the smooth connection of the TS to the reactant and the products.

    • A computational study on kinetics, mechanism and thermochemistry of gas-phase reactions of 3-hydroxy-2-butanone with OH radicals

      Nand Kishor Gour Satyendra Gupta Bhupesh Kumar Mishra Hari Ji Singh

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      Theoretical investigation has been carried out on the kinetics and reaction mechanism of the gas-phase reaction of 3-hydroxy-2-butanone (3H2B) with OH radical using dual-level procedure employing the optimization at DFT(BHandHLYP)/6-311++G(d,p) followed by a single-point energy calculation at the CCSD(T)/6-311++G(d,p) level of theory. The pre- and post reactive complexes are also validated at entrance and exit channels, respectively. Thus reaction may be proceed via indirect mechanism. The intrinsic reaction coordinate (IRC) calculation has also been performed to confirm the smooth transition from a reactant to product through the respective transition states. The rate coefficients were calculated for the first time over a wide range of temperature (250-450 K) and described by the following expression: kOH = 7.56 × 10−11exp[−(549.3 ± 11.2)/T] cm3 molecule-1s-1. At 298 K, our calculated rate coefficient 1.20 × 10−11 cm3 molecule-1 s-1 is in good agreementwith the experimental results. Our calculation indicates that H-abstraction from 𝛼-C-H site of 3H2B is the dominant reaction channel. Using group-balanced isodesmic reactions, the standard enthalpies of formation for 3H2B and radicals generated by hydrogen abstraction are reported for the first time. The branching ratios of the different reaction channels are also determined. Also, the atmospheric lifetime of 3H2B is also calculated to be 1.04 days.

    • Theoretical study on mechanism, kinetics, and thermochemistry of the gas phase reaction of 2,2,2-trifluoroethyl butyrate with OH radicals at 298 K

      Nand Kishor Gour Bhupesh Kumar Mishra Hari Ji Singh

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      A theoretical investigation has been carried out on the mechanism, kinetics, and thermochemistry of gas-phase reaction of 2,2,2-trifluoroethyl butyrate (TFEB, CH3CH2CH2C(O)OCH2CF3) with OH radicals using a modern DFT functional. The involvement of pre- and post-reactive complexes was explored and the reaction profiles were modeled. Energetic calculations were performed using the M06-2X/6-31+G(d,p) method. The intrinsic reaction coordinate (IRC) calculation has been performed to confirm the smooth transition from the reactant to product through the respective transition state. It has been found that the dominant path of the H-atom abstraction takes place from the –CH2- position, which is attached with the methyl group at the one end of TFEB. Theoretically calculated rate constant at 298 K using canonical transition state theory (CTST) is found to be in reasonable agreement with the experimental data. Using group-balanced isodesmic procedure, the standard enthalpy of formation for TFEB is reported for the first time. The branching ratios of the different reaction channels are also determined. The atmospheric lifetime of TFEB is determined to be 6.8 days.

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