• HARI JI SINGH

      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.

    • Computational studies on 1,2,4-Triazolium-based salts as energetic materials

      Rakhi Singh Hari Ji Singh S K Sengupta

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      The results of the computational studies performed on 1,2,4-triazolium cation-based salts designed by pairing it with energetic nitro-substituted 5- membered N-heterocyclic anions such as 5-nitrotetrazolate, 3,5-dinitrotriazolate, and 2,4,5 trinitroimidazolate are reported. Condensed phase heats of formation of the designed ionic salts and their thermodynamic and energetic properties have also been calculated. The results show that these salts are potential energetic materials and possess high positive heats of formation. The detonation velocity, D, and detonation pressure, P, have been calculated using the Kamlet-Jacobs equation and found to be 7–8 km/s and 25–29 GPa, respectively. These values fall in the range of the criteria to designate them as high-energy-density materials. Nucleus independent chemical shift (NICS) studies performed on the designed molecules show that these salts are stable in nature.

    • Theoretical studies on BTA-Metal (M=Ni, Cu) Complexes as High Energy Materials

      POOJA SHARMA HARI JI SINGH SOUMITRA K SENGUPTA

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      Metal complexes of Nickel and Copper with the dianion of bidentate chelating agent BTA [N,Nbis( 1(2)H-tetrazole-5-yl)-amine] along with NH₃ and NH₂NO₂ ligands were designed. A total of four metal complexes having the compositions such as M(BTA)(NH₃)(NH₂NO₂) and M(BTA)(NH2NO₂)₂whereMis the metal atom, were formulated and subjected to detailed theoretical study to explore their energetic properties. Density Functional Theory (DFT) was used to predict the optimized geometry of the complexes at TPSS/ 6-311G(d,p) level. The heats of formation of the metal complexes were determined using atomization method.Crystal densities of the salts were predicted using the data obtained at B3PW91/6-31G(d,p) level utilizing the wave function analysis (WFA) program. Results indicate that all the designed compounds possess density inthe range of 2.18–2.25 g cm⁻³. This is the remarkable feature of the title compounds because loading density is one of the desired properties for increasing the detonation performance of energetic materials. The calculatedimpact sensitivities (h₅₀, cm) show that the three of the designed compounds are comfortably insensitive towards impact (h₅₀,cm ∼42) in comparison to the experimentally determined values for the commercially used powerful explosives such as RDX (24–28 cm) and HMX (26–32 cm). Ni(BTA)(NH₂NO₂)₂, the fourth designed compound has a value almost similar to that of RDX and HMX. The calculated detonation parameters D (detonation velocity) and P (detonation pressure) are predicted to be in the range of 7.7–8.5 km s⁻¹ and 29.5–36.1 GPa, respectively. Results obtained in the present study predict that the designed compounds can be used as high energy density materials (HEDs).

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