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 atmospheric lifetime and GWPs. © 2013 American Chemical Society.

Balla Rajakumar

Department Of Chemistry

Gonu Srinivasulu

ATMOSPHERIC IMPLICATIONS

CANONICAL VARIATIONAL TRANSITION-STATE THEORIES

Degradation mechanism

GLOBAL WARMING POTENTIAL

Minimum energy paths

SMALL-CURVATURE TUNNELING

Temperature dependent

Theoretical investigations

Abstracting

Degradation

Global warming

Molecules

Reaction kinetics

Free radicals

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Physical Chemistry A

The kinetics of the reaction between pinonaldehyde (C 10H16O2) and Cl atom were studied using high level ab initio G3(MP2) and DFT based MPWB1K/6-31 + G(d) and MPW1K/6-31 + G(d) levels of theories coupled with Conventional Transition State Theory in the temperature range between 200 and 400 K. The negative temperature dependent rate expression for the title reaction obtained with Wigner’s and Eckart’s symmetrical tunneling corrections are k(T) =(5.1 ± 0.56) × 10 −19T2.35exp[(2098 ± 2)/T] cm 3 molecule −1s−1, and k(T) =(0.92 ± 0.18) × 10 −19T2.60exp[(2204 ± 4)/T] cm 3 molecule −1 s −1, respectively, at G3(MP2)//MPWB1K method. The H abstraction reaction from the –CHO group was found to be the most dominant reaction channel among all the possible reaction pathways and its corresponding rate coefficient at 300 K is k(Eckart’s unsymmetrical) = 3.86 ×10−10 cm 3 molecule −1 s −1. Whereas the channel with immediate lower activation energy is the H-abstraction from –CH- group (Tertiary H-abstraction site, C g). The rate coefficient for this channel is k Cg(Eckart’s unsymmetrical) = 1.83 ×10−15 cm 3 molecule −1 s −1 which is smaller than the dominant channel by five orders of magnitude. The atmospherically relevant parameters such as lifetimes were computed in this investigation of its reaction with Cl atom. [Figure not available: see fulltext.] © 2016, Indian Academy of Sciences.

Fulltext

Journal of Chemical Sciences

Rate coefficients for hydrogen abstraction reaction of pinonaldehyde (C10H16O2) with Cl atoms between 200 and 400 K: A DFT study

A dual-level direct dynamic method is employed to estimate the addition and hydrogen abstraction rate coefficients for the reactions of cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF with hydroxyl radicals (OH) using variational transition state theory (VTST) with interpolated single-point energies (ISPE) at CCSD(T)/cc-pVTZ//M06-2X/6-31+G(d,p) level of theory. The rate coefficients of cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF + OH reactions were computed using Canonical Variational Transition state Theory (CVT) with Small Curvature Tunneling (SCT) in the temperature range of 200-400 K. It was found that the contribution of abstraction reactions toward the overall reaction to be insignificant, and hence negligible in comparison to the addition reactions in the studied temperature range of 200-400 K. The total rate coefficient for cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF + OH reactions were calculated to be 6.83 × 10-13, 3.17 × 10-12, 5.43 × 10-13 and 2.22 × 10-13 cm3 molecule-1 s-1, respectively at 298 K. The atmospheric life times of cis-CHF=CHCHF2, trans-CHF=CHCHF2CHF, CF2=CHCHF2 and CF2=C=CHF are estimated to be 16, 3.4, 21 and 57 days respectively at 277 K. The global warming potentials (GWPs) of title molecules at the time horizons of 20, 100 and 500 years were computed using the rate coefficients and radiative forcing values obtained in this study. Since these title molecules show significantly lower GWPs than many hydrofluorocarbons (HFCs) and chlorofluorocarbons (CFCs), it is conclude that these hydrofluoro-olefines (HFOs) may be possible replacements to HFCs in many industrial applications. © 2015 Elsevier B.V. All rights reserved.

Journal of Fluorine Chemistry

Kinetic parameters for the reaction of OH radical with cis-CHF=CHCHF2, trans-CHF=CHCHF2, CF2=CHCHF2 and CF2=C=CHF: Hybrid meta DFT and CVT/SCT/ISPE calculations

The rate coefficients of hydroxyl radical (OH) reaction with limonene were computed using canonical variational transition state theory with small-curvature tunnelling between 275 and 400 K. The geometries and frequencies of all the stationary points are calculated using hybrid density functional theory methods M06-2X and MPWB1K with 6-31+G(d,p), 6-311++G(d,p), and 6-311+G(2df,2p) basis sets. Both addition and abstraction channels of the title reaction were explored. The rate coefficients obtained over the temperature range of 275-400 K were used to derive the Arrhenius expressions: k(T) = 4.06×10-34 T7.07 exp[4515/T] and k(T) = 7.37×10-25 T3.9 exp[3169/T] cm3 molecule-1 s-1 at M06-2X/6-311+G(2df,2p) and MPWB1K/6-311+G(2df,2p) levels of theory, respectively. Kinetic study indicated that addition reactions are major contributors to the total reaction in the studied temperature range. The atmospheric lifetime (τ) of limonene due to its reactions with various tropospheric oxidants was calculated and concluded that limonene is lost in the atmosphere within a few hours after it is released. The ozone production potential of limonene was computed to be (14-18) ppm, which indicated that degradation of limonene would lead to a significant amount of ozone production in the troposphere. © 2015 Taylor & Francis.

Molecular Physics

Theoretical investigations of the gas phase reaction of limonene (C10H16) with OH radical

The gas phase temperature dependent rate coefficients of Cl atoms with 2,2,2-trifluoroethylbutyrate, CH<inf>3</inf>CH<inf>2</inf>CH<inf>2</inf>C(O)OCH<inf>2</inf>CF<inf>3</inf>, were measured in the temperature range 268-343 K, at atmospheric pressures using the relative rate method, with ethyl acetate and ethane as reference compounds. The temperature dependent rate coefficients for the reaction of 2,2,2-TFEB + Cl were measured and were used to deduce the Arrhenius expression: k<inf>268-343K</inf> = [(4.42 ± 0.01) × 10-19]T2.6 exp{(1132 ± 566)/T} cm3 molecule-1 s-1. At 298 K, the rate coefficient for the title reaction is (4.54 ± 2.87) × 10-11 cm3 molecule-1 s-1, which is in good agreement with a previously reported value at 298 K. To complement our experimental results over the studied temperature range, theoretical kinetic calculations were also performed for the title reaction using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) corrections in combination with the CCSD(T)/cc-pVDZ//M062X/6-31+g(d,p) level of theory. The temperature dependent Arrhenius expression was obtained to be k(T) = (1.89 ± 2.64) × 10-21T3.4 exp{(1321 ± 111)/T} cm3 molecule-1 s-1. The branching ratios, atmospheric implications, and degradation mechanism of 2,2,2-trifluoroethylbutyrate, CH<inf>3</inf>CH<inf>2</inf>CH<inf>2</inf>C(O)OCH<inf>2</inf>CF<inf>3</inf>, were discussed in detail in this manuscript. (Graph Presented). © 2015 American Chemical Society.

Gas Phase Kinetics of 2,2,2-Trifluoroethylbutyrate with the Cl Atom: An Experimental and Theoretical Study

Thermal decomposition of methyl butanoate (MB) diluted in argon was studied behind reflected shock waves in the temperature range of 1229-1427 K using a single pulse shock tube (SPST). The post shock mixtures were analyzed quantitatively using gas chromatography (GC) and qualitatively using Fourier-transform infrared (FTIR) spectroscopy. Methane (CH4), ethylene (C2H4), and acetylene (C2H2) were the major decomposition products. The minor products are ethane (C2H6), propylene (C3H6), 1,3-butadiene (C4H6) and methyl acrylate (C4H6O2). The obtained first order rate coefficient for the decomposition of MB is ktotal (1229-1427 K) = (3.08 ± 1.11) × 1012exp(-(53.6 kcal mol-1 ± 4.7)/RT) s-1, and for the formation of C2H4, the rate coefficient was found to be kethylene (1229-1427 K) = (7.92 ± 2.72) × 109exp(-(47.6 kcal mol-1 ± 4.5)/RT) s-1. Theoretical kinetic calculations were also performed for the unimolecular hydrogen transfer reactions using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) corrections. The temperature dependent rate coefficients for the overall reaction were computed in the temperature range of 500-2500 K, and were used to derive the Arrhenius expression: ktheorytotal (500-2500 K) = (9.05 ± 1.91) × 1013exp(-(70.7 kcal mol-1 ± 2.0)/RT) s-1. A reaction scheme containing 39 species and 66 elementary reactions was proposed to simulate the reactant and product concentrations over the temperature range of 1229-1427 K. The agreement between the experimental results and the model prediction for all the species is observed to be good. The decomposition of MB happens mostly via intramolecular hydrogen transfer than C-C bond and C-O bond fission. The majority of these intramolecular hydrogen transfer reactions are lower energy barrier reactions than the homolytic bond fission reactions. © The Royal Society of Chemistry.

RSC Advances

Experimental and theoretical study on thermal decomposition of methyl butanoate behind reflected shock waves

The kinetics and abstraction rate coefficients of hydroxyl radical (OH) reaction with pinonaldehyde were computed using G3(MP2) theory and transition-state theory (TST) between 200 and 400 K. Structures of the reactants, reaction complexes (RCs), product complexes (PCs), transition states (TSs), and products were optimized at the MP2(FULL)/6-31G* level of theory. Fifteen transition states were identified for the title reaction and confirmed by intrinsic reaction coordinate (IRC) calculations. The contributions of all the individual hydrogens in the substrate molecule to the total reaction are computed. The quantum mechanical tunneling effect was computed using Wigner's and Eckart's methods (both symmetrical and unsymmetrical methods). The reaction exhibits a negative temperature dependent rate coefficient, k(T) = (1.97 ± 0.34) × 10 -13 exp[(1587 ± 48)/T] cm 3 molecule -1 s -1, k(T) = (3.02 ± 0.56) × 10 -13 exp[(1534 ± 52/T] cm 3 molecule -1 s -1, and k(T) = (4.71 ± 1.85) × 10 -14 exp[(2042 ± 110)/T] cm 3 molecule -1 s -1 with Wigner's, Eckart's symmetrical, and Eckart's unsymmetrical tunneling corrections, respectively. Theoretically calculated rate coefficients are found to be in good agreement with the experimentally measured ones and other theoretical results. It is shown that hydrogen abstraction from -CHO position is the major channel, whereas H-abstraction from -COCH 3 is negligible. The atmospheric lifetime of pinonaldehyde is computed to be few hours and found to be in excellent agreement with the experimentally estimated ones. © 2012 American Chemical Society.

Abstraction kinetics of H-atom by OH radical from pinonaldehyde (C 10H 16O 2): Ab initio and transition-state theory calculations

The rate coefficients of ((E)-CF 3CH=CHF, (Z)-CF 3CH=CHF, (E)-CF 3CF=CHF, and (Z)-CF 3CF=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 3CH=CHF, (Z)-CF 3CH=CHF, (E)-CF 3CF=CHF, and (Z)-CF 3CF=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 3CH=CHF, (Z)-CF 3CH=CHF, (E)-CF 3CF=CHF, and (Z)-CF 3CF=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. © 2012 American Chemical Society.

Rate coefficients and reaction mechanism for the reaction of OH radicals with (E)-CF 3CH=CHF, (Z)-CF 3CH=CHF, (E)-CF 3CF=CHF, and (Z)-CF 3CF=CHF between 200 and 400 K: Hybrid density functional theory and canonical variational transition state theory calculations

The rate coefficients for the reaction OH + CH3CH 2CH2OH → products (k1)and OH + CH 3CH(OH)CH3 → products (k2) were measured by the pulsed-laser photolysis-laser- induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k1 and k2 are as follows: k1 = (6.2 ± 0.8) × 10-12 exp[-(10 ± 30)/T ]cm3 molecule-1 s-1, with k1 (298 K) = (5.90 ± 0.56) × 10-12 cm3 molecule-1 s-1,and k2 = (3.2 ± 0.3) × 10-12 exp[(150 ± 20)/T ]cm3 molecule-1 s-1, with k2 (298) = (5.22 ± 0.46) × 10-12 cm3 molecule-1 s-1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n-propanol and iso-propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10-19 and (1.90 ± 0.10) × 10-18 cm2 molecule-1, respectively. The atmospheric implications of the degradation of n-propanol and iso-propanol are discussed. © 2009 Wiley Periodicals, Inc.

Journal	Journal of Physical Chemistry A
ISSN	10895639
Open Access	No