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Rajakumar Balla
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Rajakumar Balla
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Rajakumar Balla
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Rajakumar, Balla
Rajakumar, B.
Balla, Rajakumar
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87 results
Now showing 1 - 10 of 87
- PublicationTheoretical investigations on the OH radical mediated kinetics of cis- and trans-CH3CF=CHF and CH3CH=CF2 over temperature range of 200-400K(01-10-2021)
;Gupta, Parth ;Jabeen, FakhraGlobal reactivity for the OH-radical mediated kinetics of three Hydrofluoroolefins (HFOs), cis-CH3CF=CHF, trans-CH3CF=CHF and CH3CH=CF2 was evaluated at the CCSD(T)/cc-pVTZ//M062x/6-31G+(d,p) level of theory. The overall kinetics was computed using the Canonical Variational Transition State Theory (CVT) in combination with Small Curvature Tunneling (SCT) and Interpolated Single Point Energy (ISPE) corrections over the temperature range of 200 and 400 K. The total rate coefficients (k, in units of cm3 molecule−1 sec−1) for the reaction of OH radical with these HFOs at 298 K were computed to be, k298Kcis−CHF=CFCH3+OH=1.69×10−12, k298Ktrans−CHF=CFCH3+OH=3.12×10−12, and k298KCF2=CHCH3+OH=5.40×10−12. To further corroborate the computed kinetics, thermodynamic parameters and branching ratios were also computed for all the reaction pathways. Atmospheric lifetimes, Radiative forcing (RF), Global Warming Potentials (GWP) and Photochemical Ozone Creation Potentials (POCP) of these HFOs were also calculated and are presented in this manuscript. - PublicationAn Exprimental and Computational Study on the Cl Atom Initiated Photo-Oxidization Reactions of Butenes in the Gas Phase(27-07-2017)
;Vijayakumar, S.Temperature-dependent rate coefficients for the reactions of Cl atoms with trans-2-butene and isobutene were measured over the temperature range of 263-363 K using relative rate technique with reference to 1,3-butadiene, isoprene, and 1-pentene. The measured rate coefficients for the reactions of Cl atoms with isobutene and trans-2-butene are kR1298K= (3.43 ± 0.11) × 10-10 and kR2298K = (3.20 ± 0.04) × 10-10 cm3 molecule-1 s-1, respectively, at 298 K and 760 torr. Measured rate coefficients were used to fit the Arrhenius equations, which are obtained to be kR1-Exp269-363K = (4.99 ± 0.42) × 10-11 exp[(584 ± 26)/T] and kR2-Exp269-363K = (1.11 ± 0.3) × 10-10 exp[(291 ± 88)/T] cm3 molecule-1 s-1 for isobutene and trans-2-butene, respectively. To understand the reaction mechanism, estimate the contribution of each reaction site, and to complement our experimental results, computational studies were also performed. Canonical variational transition state theory with small curvature tunneling in combination with MP2/6-31G(d), MP2/6-31G(d,p), MP2/6-31+G(d,p), CCSD(T)/cc-pvdz, and QCISD(T)/cc-pvdz level of theories were used to calculate the temperature-dependent rate coefficients over the temperature range of 200-400 K. The effective lifetimes, thermodynamic parameters, and atmospheric implications of the test molecules were also estimated. - PublicationKinetic and Mechanistic Investigation for the Gas-Phase Tropospheric Photo-oxidation Reactions of 2,2,2-Trifluoroethyl Acrylate with OH Radicals and Cl Atoms(26-03-2020)
;Kumar, AvinashThe photo-oxidation of 2,2,2-trifluoroethyl acrylate (TFEA) (CH2CHC(O)OCH2CF3) initiated by OH radicals and Cl atoms was investigated in tropospheric conditions using both experimental and computational methods. The kinetic measurements were carried out in the temperature range of 268-363 K using the relative rate method. The rate coefficients for the reaction of OH radicals with TFEA were measured relative to diethyl ether, ethylene, and acetaldehyde. The rate coefficients for the reaction of Cl atoms with TFEA were measured relative to propylene and ethylene. The rate coefficients for the reaction of TFEA with OH radicals and Cl atoms at 298 K were experimentally measured to be kR1exp - 298 K = (1.41 ± 0.31) × 10-11 cm3 molecule-1 s-1 and kR2exp - 298 K = (2.37 ± 0.50) × 10-10 cm3 molecule-1 s-1, respectively. The deduced temperature-dependent Arrhenius expressions for the reactions of OH radicals and Cl atoms with TFEA are kR1exp - (268 - 363 K) = (9.82 ± 1.37) × 10-12 exp. [(812 ± 152)/T] cm3 molecule-1 s-1 and kR2exp - (268 - 363 K) = (1.25 ± 0.17) × 10-11 exp. [(862 ± 85)/T] cm3 molecule-1 s-1, respectively. To complement our experimental results, computational calculations were performed at CCSD(T)/cc-pVDZ//M062X/6-31+G(d,p) and CCSD(T)/cc-pVDZ//MP2/6-311+G(d,p) levels of theory, respectively, in combination with canonical variational transition-state theory (CVT) with small curvature tunneling (SCT) over the temperature range of 200-400 K. Furthermore, the degradation mechanisms initiated by OH radicals and Cl atoms were proposed for the titled reactions based on the qualitative analysis of the products in gas chromatography-mass spectrometry (GC-MS) and gas chromatography-infrared spectroscopy (GC-IR). Atmospheric implications, thermochemistry, and branching ratios for the titled reactions are discussed in detail in the paper. - PublicationTemperature-dependent kinetic study of the photo-oxidation reaction of vinyl butyrate with Cl atoms and fate of the formation of alkoxy radicals(16-05-2021)
;Kaipara, Revathy ;Kumar, Avinash ;Gupta, ParthRR-GC-FID technique was used to investigate the rate coefficient (k) for the reaction of vinyl butyrate (VB) with Cl atoms in the temperature range of 268 and 363 K at 760 Torr of N2. The k at 298 K was measured to be k298KVB+Cl=2.57±0.68×10-10 cm3 molecule−1 s−1. To comprehend the reaction pathway, and kinetic parameters associated with the title reaction were assessed computationally using CVT/SCT/ISPE method at CCSD(T)//MP2/6-311++G(d,p) level of theory. Product analysis was performed using GC–MS and GC-IR. Cumulative Atmospheric Lifetime (CAL), Radiative Forcing (RF), Global Warming Potential (GWP) and Photochemical Ozone Creation Potential (POCP) were estimated. - PublicationOxidative Degradation Kinetics and Mechanism of Two Biodiesel Constituents (Ethyl-2-Methyl Propionate (E2MP) and Ethyl-2,2-Dimethyl Propionate (E22DMP)) Initiated by Cl Atoms(16-01-2020)
;Kaipara, RevathyThe oxidative reaction kinetics and mechanism of ethyl-2-methyl propionate (E2MP) and ethyl-2,2-dimethyl propionate (E22DMP) initiated by Cl atoms were investigated both experimentally and computationally. Temperature-dependent kinetic studies on the reaction of E2MP and E22DMP with Cl atoms were carried out using a relative rate technique over the temperature range of 268-363 K and at 760 Torr. The rate coefficients of both reactions at 298 K were measured (using IUPAC recommended reference rate coefficients) to be kE2MP+Cl298K = (7.19 ± 1.60) × 10-11 cm3 molecule-1 s-1 and kE22DMP+Cl298K = (5.87 ± 1.33) × 10-11 cm3 molecule-1 s-1, respectively. In addition to complement our experimental results, the kinetics were computed at the CCSD(T)/MG3S//BHandHLYP/6-311+G(d,p) level of theory over the temperature range of 200-400 K using the canonical variational transition state theory in conjunction with small curvature tunneling and interpolated single-point energy. Furthermore, the product degradation of the studied esters with Cl atoms was performed using gas chromatography coupled with mass spectrometry and gas chromatography coupled with infrared spectroscopy as analytical tools. The plausible product degradation mechanisms were proposed, and carbonyl compounds were found to be the major products from the degradation of studied esters. Atmospheric lifetimes of both esters were estimated with respect to the concentrations of Cl atoms in both ambient and marine boundary layer conditions. - PublicationShock tube study and RRKM calculations on thermal decomposition of 2-chloroethyl methyl ether(01-01-2017)
;Parandaman, A.The thermal decomposition of 2-chloroethyl methyl ether (2-CEME) was studied in the temperatures between 1175 and 1467 K. The decomposition of 2-CEME happens predominantly via molecular elimination reactions than via C–C and C–O bond fission channels. The major decomposition products are methane, ethylene and methanol. The minor are acetaldehyde and ethane. The Arrhenius expression for the overall decomposition of 2-CEME was obtained to be ktotalexp(1175−1467K)=(4.12±0.42)×1011exp(−(52.2kcalmol−1±2.6)/RT)s−1. To simulate the distribution of reactant and products over the experimentally studied temperatures between 1175 and 1467 K, a reaction scheme was constructed with 45 species and 71 elementary reactions. The pressure and temperature dependent rate coefficients were calculated for various unimolecular dissociation pathways in 2-CEME using RRKM theory. The high pressure limit temperature dependent rate coefficient for the total decomposition of 2-CEME was obtained to be ktotalCCSDT//M06−2X(500–2000 K) = (2.55 ± 0.21) × 1014 exp (−(67.6 kcal mol−1± 3.0)/RT) s−1. - PublicationInvestigation of kinetics and mechanistic insights of the reaction of criegee intermediate (CH2OO) with methyl-ethyl ketone (MEK) under tropospherically relevant conditions(01-01-2023)
;Debnath, AmitThe temperature-dependent kinetics was investigated for the reaction of the simplest Criegee intermediate (CH2OO) with Methyl-ethyl ketone (CH3COC2H5, MEK). A direct method was employed to measure the rate of change of the concentration of CH2OO using a highly sensitive Pulsed Laser Photolysis-Cavity Ring-down Spectroscopy (PLP-CRDS) technique. The temperature dependent rate coefficient obtained for the CH2OO + MEK reaction was k4(T = 258–318 K) = (1.26 ± 0.16) × 10−14 × exp{(1179.1 ± 71.8)/T} cm3 molecule−1 s−1 and the rate coefficient at room temperature was k4(298 K) = (6.39 ± 0.20) × 10−13 cm3 molecule−1 s−1 at 50 Torr/N2. Theoretical calculations were performed to predict the reaction mechanism and probable end products. The secondary ozonide (SOZ) formation pathway was found to be the rate determining step, which gets decomposed into HCOOH and MEK as the major products. Both experimental and theoretical results show a negative T-dependency in the studied range. - PublicationExperimental and Theoretical Investigation of Reactions of Formyl (HCO) Radicals in the Gas Phase: (I) Kinetics of HCO Radicals with Ethyl Formate and Ethyl Acetate in Tropospherically Relevant Conditions(15-09-2022)
;Mondal, KoushikFormyl (HCO) radicals were generated in situ in the gas phase via the photolysis of glyoxal in N2 at 248 nm using the pulsed laser photolysis-cavity ring-down spectrometry technique, and the absorption cross-section of the radical was measured to be σHCO = (5.3 ± 0.9) × 10-19 cm2 molecule-1 at 298 K and 615.75 nm, which was the probing wavelength. The kinetics of the reactions of HCO radicals with ethyl formate (EF) and ethyl acetate (EA) were investigated experimentally in the temperature range of 260-360 (±2) K at a pressure of 60 Torr/N2. The absolute rate coefficient for the reaction between HCO and EF was measured to be kHCO+EFExpt(298 K) = (1.39 ± 0.30) × 10-14 cm3 molecule-1 s-1 at ambient temperature, whereas that for the reaction of HCO with EA was measured tobe kHCO+EATheory(298 K) = (2.05 ± 0.43) × 10-14 cm3 molecule-1 s-1. The reaction of HCO with EA was faster than that with EF, which might be due to the greater stability of the formed radical intermediate due to hyperconjugative and inductive effects. The dependency of the measured kinetics on experimental pressures and laser fluences was examined within a certain range. To complement the experiments, kinetics of the title reactions in the temperature range of 200-400 K were deciphered theoretically via the canonical variational transition-state theory with small-curvature tunneling and interpolated single-point energy (CVT/SCT/ISPE) method using a dual-level approach at the CCSD(T)/cc-pVTZ//MP2/6-311++G(d,p) level of theory/basis set. A good degree of agreement was detected between the rate coefficients measured experimentally and those calculated theoretically both at room temperature and throughout the range of temperatures studied. The kinetic branching ratios and thermochemistry of the reactions were investigated to understand the thermodynamic feasibility and kinetic lability of each pathway throughout the studied temperatures. Atmospheric implications of these reactions of HCO radicals are also discussed. - PublicationKinetics of the thermal decomposition of tetramethylsilane behind the reflected shock waves between 1058 and 1194 K(01-04-2016)
;Parandaman, A.Thermal decomposition of tetramethylsilane (TMS) diluted in argon was studied behind the reflected shock waves in a single pulse shock tube (SPST) in the temperature range of 1058-1194 K. The major products formed in the decomposition are methane (CH 4) and ethylene (C 2 H 4); whereas ethane and propylene were detected in lower concentrations. The decomposition of TMS seems to be initiated via Si-C bond scission by forming methyl radicals (CH 3) and trimethylsilyl radicals ((CH 3) 3Si). The total rate coefficients obtained for the decomposition of TMS were fit to Arrhenius equation in two different temperature regions 1058-1130 K and 1130-1194 K. The temperature dependent rate coefficients obtained are k total (1058-1130 K) = (4.61±0.70) ×1018 exp (-(79.9 kcal mol -1±3.5)/RT) s -1, k total (1130-1194 K) = (1.33 ± 0.19) ×106 exp (-(15.3 kcal mol -1±3.5)/RT) s -1. The rate coefficient for the formation of CH 4 is obtained to be k methane (1058-1194 K) = (4.36 ± 1.23) ×1014 exp (-(61.9 kcal mol -1±4.9)/RT) s -1. A kinetic scheme containing 21 species and 38 elementary reactions was proposed and simulations were carried out to explain the formation of all the products in the decomposition of tetramethylsilane. - PublicationThermochemistry and Kinetic Studies on the Autoignition of 2-Butanone: A Computational Study(26-07-2018)
;Kuzhanthaivelan, S.Unimolecular reactions of alkylperoxy(ROO•), hydroperoxyalkyl(•QOOH), and hydroperoxyalkylperoxy(•OOQOOH) radicals of 2-butanone, which is a potential biofuel molecule, have been studied computationally. These radicals are responsible for the chain branching at low temperature oxidation and play a significant role in modeling the autoignition. The composite CBS-QB3 method was used to study the thermochemistry and energetics of all the species involved. Intrinsic reaction coordinate (IRC) calculations were carried out for all the transition states along various reaction pathways. All the possible reactions like H-migration, •OH elimination, and HO•2 elimination reactions were studied for these radicals. It was found that, the isomerization of •OOQOOH to HOOQOO• is the most favorable channel, which involves 8- and 9-membered cyclic transition states. However, the decomposition pathway involves the H-migration from carbon to oxygen. The mechanism for the decomposition of all •OOQOOH radicals with their potential energy level diagrams are reported. The temperature dependent rate coefficients were also studied using Canonical Variational Transition state theory (CVT) with small curvature tunneling (SCT) in the temperature range of 400-1500 K, which is relevant to the combustion. Thermodynamic parameters for all the reactions involved were calculated. The high barrier (1,3 H-migration) reactions were found to be exothermic and spontaneous, which is unexpected.