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Balla Rajakumar

Bio: Balla Rajakumar is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Arrhenius equation & Chemical kinetics. The author has an hindex of 14, co-authored 93 publications receiving 679 citations. Previous affiliations of Balla Rajakumar include Indian Institute of Science & University of Colorado Boulder.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors reported measurements of the CH3CO quantum yield, Φ C H 3 CO, following the 248-nm pulsed laser photolysis of acetone (CH3C(O)CH3), methyl ethyl ketone, and biacetyl.
Abstract: We report measurements of the CH3CO quantum yield, Φ C H 3 CO , following the 248 nm pulsed laser photolysis of acetone (CH3C(O)CH3), methyl ethyl ketone (CH3C(O)CH2CH3), and biacetyl (CH3C(O)C(O)CH3). CH3CO quantum yields at 248 nm were measured at 296 K, relative to CH3CO reference systems. CH3CO was detected using cavity ring-down spectroscopy at wavelengths between 490 and 660 nm. Measurements were performed between 60 and 670 Torr (He, N2 bath gases) and the obtained CH3CO quantum yields in the low-pressure limit, Φ C H 3 CO 0 , were 0.535 ± 0.09, 0.41 ± 0.08, and 0.76 ± 0.11, for acetone, methyl ethyl ketone, and biacetyl, respectively. The quoted uncertainties are 2σ (95% confidence level) and include estimated systematic errors. An increase in Φ C H 3 CO with increasing bath gas pressure, which depended on the identity of the collision partner (He, N2), was observed. The present results are compared with previous quantum yield determinations.

37 citations

Journal ArticleDOI
TL;DR: This compound can be suggested as an acceptable substitute to HFCs in terms of its atmospheric lifetime and GWPs, and the atmospheric implications and the degradation mechanism of CF3CH(OH)CF3 are discussed.
Abstract: The kinetic studies of the H-abstraction reaction of CF3CH(OH)CF3 with the OH radical, which is predicted to have two classes of possible reaction channels, were carried out. The minimum energy path and energetics were calculated at M062X/6-31+G (d,p) method. The rate coefficients for each reaction channels were evaluated by canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT) and zero-curvature tunneling over the wide range of temperature of 200–3000 K. The temperature-dependent rate expression for the title reaction is obtained to be k(Total) = 2.60 × 10–22T3.04 exp(372.45/T) cm3 molecule–1 s–1; with k(298) = 3.54 × 10–14 cm3 molecule–1 s–1. The global warming potentials (GWPs) and atmospheric lifetimes of CF3CH(OH)CF3 are computed in the present investigation. The atmospheric implications and the degradation mechanism of CF3CH(OH)CF3 are discussed. It is concluded that this compound can be suggested as an acceptable substitute to HFCs in terms of its a...

32 citations

Journal ArticleDOI
TL;DR: In this article, the authors reported ab intio, DFT and transition state theory (TST) calculations on HF, HCl and ClF elimination reactions from CH2Cl-CH2F molecule.
Abstract: This paper reports ab intio, DFT and transition state theory (TST) calculations on HF, HCl and ClF elimination reactions from CH2Cl–CH2F molecule. Both the ground state and the transition state for HX elimination reactions have been optimized at HF, MP2 and DFT calculations with 6-31G*, 6-31G** and 6-311++G** basis sets. In addition, CCSD(T) single point calculations were carried out with MP2/6-311++G** optimized geometry for more accurate determination of the energies of the minima and transition state, compared to the other methods employed here. Classical barriers are converted to Arrhenius activation energy by TST calculations for comparisons with experimental results. The pre-exponential factors, A, calculated at all levels of theory are significantly larger than the experimental values. For activation energy, Ea, DFT gives good results for HF elimination, within 4–8 kJ mol−1 from experimental values. None of the methods employed, including CCSD(T), give comparable results for HCl elimination reactions. However, rate constants calculated by CCSD(T) method are in very good agreement with experiment for HCl elimination and they are in reasonable agreement for HF elimination reactions. Due to the strong correlation between A and Ea, the rate constants could be fit to a lower A and Ea (as given by experimental fitting, corresponding to a tight TS) or to larger A and Ea (as given by high level ab initio calculations, corresponding to a loose TS). The barrier for ClF elimination is determined to be 607 kJ mol−1 at HF level and it is unlikely to be important for CH2FCH2Cl. Results for other CH2X–CH2Y (X,Y = F/Cl) are included for comparison.

31 citations

Journal ArticleDOI
TL;DR: The atmospheric lifetimes and global warming potentials of the test molecules were computed using the rate coefficients obtained in this study and it is concluded that these molecules are very short-lived in the Earth's atmosphere with low GWPs.
Abstract: The rate coefficients of ((E)-CF(3)CH═CHF, (Z)-CF(3)CH═CHF, (E)-CF(3)CF═CHF, and (Z)-CF(3)CF═CHF) + OH reactions were computed using M06-2X/6-31+G(d,p) theory in the temperature range of 200 and 400 K. The possible reaction mechanisms of the ((E)-CF(3)CH═CHF, (Z)-CF(3)CH═CHF, (E)-CF(3)CF═CHF, and (Z)-CF(3)CF═CHF) + OH reactions were examined. The rate coefficients for the addition and abstraction reactions were calculated using canonical variational transition state theory (CVT) and conventional transition state theory (CTST), respectively, and we concluded that abstraction reactions are negligible within the temperature range and addition reactions take the lead role. The small curvature tunnelling (SCT) was included in the computation of the rate coefficients. The temperature dependent rate expressions (in cm(3) molecule(-1) s(-1)) of the (E)-CF(3)CH═CHF, (Z)-CF(3)CH═CHF, (E)-CF(3)CF═CHF, and (Z)-CF(3)CF═CHF + OH reactions between 200 and 400 K are presented. The atmospheric lifetimes and global warming potentials (GWPs) of the test molecules were computed using the rate coefficients obtained in this study, and it is concluded that these molecules are very short-lived in the Earth's atmosphere with low GWPs.

26 citations

Journal ArticleDOI
TL;DR: In this article, the unimolecular elimination of HCl from 1,2-dichloroethane (1-DCE) has been studied in the temperature range of 10501175 K behind reflected shock waves in a single pulse shock tube.
Abstract: Thermal decomposition of 1,2-dichloroethane (1,2-DCE) has been studied in the temperature range of 10501175 K behind reflected shock waves in a single pulse shock tube. The unimolecular elimination of HCl is found to be the major channel through which 1,2-DCE decomposes under these conditions. The rate constant for the unimolecular elimination of HCl from 1,2-dichloroethane is found to be 10(13.98+/-0.80) exp(-57.8+/-2.0/RT) s(-1), where the activation energy is given in kcal mol(-1) and is very close to that value for CH3CH2Cl (EC). Ab initio (HF and MP2) and DFT calculations have been carried out to find the activation barrier and the structure of the transition state for this reaction channel from both EC and 1,2-DCE. The preexponential factors calculated at various levels of theory (BF/6-311++G**, MP2/6-311++G**, and B3LYP/6-311++G**) are (approximate to10(15) s(-1)) significantly larger than the experimental results. If the torsional mode in the ground state is treated as free internal rotation the preexponential factors reduce significantly, giving excellent agreement with experimental values. The DFT results are in excellent (fortuitous?) agreement with the experimental value for activation energy for 1,2-DCE while the MP2 and HF results seem to overestimate the barrier. However, DFT results for EC is 4.5 kcal mol(-1) less than the previously reported experimental values. At all levels, theory predicts an increase in HCI elimination barrier on beta-Cl substitution on EC.

26 citations


Cited by
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Book ChapterDOI
01 Jan 2014
TL;DR: Myhre et al. as discussed by the authors presented the contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) 2013: Anthropogenic and Natural Radiative forcing.
Abstract: This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)

3,684 citations

01 Feb 1995
TL;DR: In this paper, the unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio using DFT, MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set.
Abstract: : The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

1,652 citations

Journal ArticleDOI
TL;DR: A detailed overview of recent results on alcohol combustion can be found in this paper, with a particular emphasis on butanols and other linear and branched members of the alcohol family, from methanol to hexanols.

676 citations

Journal ArticleDOI
TL;DR: The most comprehensive review of the radiative efficiencies and global warming potentials of halogenated compounds performed to date can be found in this article, where the authors provide a comprehensive and self-consistent set of new calculations of radiative efficiency for these compounds, mostly employing atmospheric lifetimes taken from the available literature.
Abstract: [1] In the mid-1970s, it was recognized that chlorofluorocarbons (CFCs) were strong greenhouse gases that could have substantial impacts on radiative forcing of climate change, as well as being substances that deplete stratospheric ozone. Around a decade later, this group of radiatively active compounds was expanded to include a large number of replacements for ozone-depleting substances such as chlorocarbons, hydrochlorocarbons, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), bromofluorocarbons, and bromochlorofluorocarbons. This paper systematically reviews the published literature concerning the radiative efficiencies (REs) of CFCs, bromofluorocarbons and bromochlorofluorocarbons (halons), HCFCs, HFCs, PFCs, sulfur hexafluoride, nitrogen trifluoride, and related halogen containing compounds. In addition, we provide a comprehensive and self-consistent set of new calculations of REs and global warming potentials (GWPs) for these compounds, mostly employing atmospheric lifetimes taken from the available literature. We also present global temperature change potentials for selected gases. Infrared absorption spectra used in the RE calculations were taken from databases and individual studies and from experimental and ab initio computational studies. Evaluations of REs and GWPs are presented for more than 200 compounds. Our calculations yield REs significantly (> 5%) different from those in the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) for 49 compounds. We present new RE values for more than 100 gases which were not included in AR4. A widely used simple method to calculate REs and GWPs from absorption spectra and atmospheric lifetimes is assessed and updated. This is the most comprehensive review of the radiative efficiencies and global warming potentials of halogenated compounds performed to date.

375 citations

Journal ArticleDOI
TL;DR: An up-to-date review of the literature available on the subject of ethanol to ethylene can be found in this paper, where the authors present an overview of the current state-of-the-art in this area.
Abstract: This article is an up-to-date review of the literature available on the subject of ethanol to ethylene. The process of ethanol to ethylene has broad development prospects. Compared with the process of petroleum to ethylene, ethanol dehydration to ethylene is economically feasible. Researchers have been redirecting their interest to the ethylene production process, catalysts, and reaction mechanisms. A fluidized bed reactor, together with a wear-resistant, efficient, and stable catalyst will be the focus of future research that includes a deep understanding of the large-scale activated alumina catalyst and the molecular sieve catalyst used, and will promote the development of the ethanol dehydration to ethylene process and provide strong support for the market competiveness of the process.

337 citations