Binod R Giri

The University of Calgary, Calgary, Alberta, Canada

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Publications (22)55.72 Total impact

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    ABSTRACT: A detailed theoretical analysis of the reaction of atomic bromine with tetrahydropyran (THP, C5H10O) was performed using several ab initio methods and statistical rate theory calculations. Initial geometries of all species involved in the potential energy surface of the title reaction were obtained at the B3LYP/cc-pVTZ level of theory. These molecular geometries were re-optimized using three different meta-generalized gradient approximation (meta-GGA) functionals. Single-point energies of the stationary points were obtained by employing the coupled-cluster with single and double excitations (CCSD) and fourth-order Møller-Plesset (MP4 SDQ) levels of theory. The computed CCSD and MP4(SDQ) energies for optimized structures at various DFT functionals were found to be consistent within 2 kJ mol-1. For a more accurate energetic description, single-point calculations at the CCSD(T)/CBS level of theory were performed for the minimum structures and transition states optimized at the B3LYP/cc-pVTZ level of theory. Similar to other ether + Br reactions, it was found that the tetrahydropyran + Br reaction proceeds in an overall endothermic addition-elimination mechanism via a number of intermediates. However, the reactivity of various ethers with atomic bromine was found to vary substantially. In contrast to the 1,4-dioxane + Br reaction, the chair form of the addition complex (c-C5H10O--Br) for THP + Br does not need to undergo ring inversion to form a boat conformer (b-C4H8O2--Br) before the intra-molecular H-shift can occur to eventually release HBr. Instead, a direct, yet more favorable route was mapped out on the potential energy surface of the THP + Br reaction. The rate coefficients for all the relevant steps involved in the reaction mechanism were computed using the energetics of coupled cluster calculations. Based on the results of the CCSDD(T)/CBS//B3LYP/cc-pVTZ level of theory, the calculated overall rate coefficients can be expressed as: kov.,calc.(T) = 4.60 × 10-10 exp[-20.4 kJ mol-1/(RT)] cm3 molecule-1 s-1 for the temperature range of 273 K to 393 K. The calculated values are found to be in excellent agreement with the experimental data published earlier.
    The Journal of Physical Chemistry A 02/2015; 119:933-942. DOI:10.1021/jp510987q · 2.78 Impact Factor
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    ABSTRACT: Absolute rate coefficients for the reaction of OH radical with propene (C3H6) and five deuterated isotopes, propene-1-D1 (CDHCHCH3), propene-1,1-D2 (CD2CHCH3), propene-112-D3 (CD2CDCH3), propene-3,3,3-D3 (CH2CHCD3), and propene-D6 (C3D6), were measured behind reflected shock waves over the temperature range of 818 – 1460 K and pressures near 1 atm. The reaction progress was followed by monitoring OH radical near 306.7 nm using UV laser absorption. Kinetic isotope effects in the measured rate coefficients are discussed and rationalized for the site-specific H abstraction by OH radical. The first experimental measurements for the branching ratio of the title reaction are reported and compared with transition state theory calculations. The allylic H-atom abstraction of propene by OH radicals was found to be the most dominant reaction pathway followed by propen-1-yl and propen-2-yl channels over the entire temperature range of this study. The derived Arrhenius expressions for various site-specific rate coefficients over 818 – 1442 K are (the subscript in the rate coefficient identifies the position of H or D atom according to the IUPAC nomenclature of alkenes): k_(3,H)=2.32×〖10〗^(-11) exp(-2341 K/T) 〖cm〗^3 〖molecule〗^(-1) s^(-1) k_(3,D)=1.96×〖10〗^(-11) exp(-2420 K/T) 〖cm〗^3 〖molecule〗^(-1) s^(-1) k_(1,H)=1.39×〖10〗^(-11) exp(-2270 K/T) 〖cm〗^3 〖molecule〗^(-1) s^(-1) k_(1,D)=1.95×〖10〗^(-11) exp(-2868 K/T) 〖cm〗^3 〖molecule〗^(-1) s^(-1) k_(2,H)=7.2×〖10〗^(-12) exp(-2282 K/T) 〖cm〗^3 〖molecule〗^(-1) s^(-1) k_(2,D)=7.69×〖10〗^(-12) exp(-2575 K/T) 〖cm〗^3 〖molecule〗^(-1) s^(-1)
    Physical Chemistry Chemical Physics 12/2014; 17(4). DOI:10.1039/C4CP04322G · 4.20 Impact Factor
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    ABSTRACT: Until recently, there was a substantial lack of reliable viscosity data for H2S, making the regression of an accurate H2S viscosity model significantly difficult. To derive a model for engineering applications (2008 H2S model), a corresponding states approach that related molecules of similar shape to H2S was applied to cover regions where no experimental data was available. Recently, new primary low-density experimental data and derived theoretical information have been published. Additionally, new high-pressure H2S viscosity measurements [at (373.15 and 423.15) K and up to 100 MPa] have also been reported. Based on this, a new revised correlation for the viscosity of H2S is presented in this work. The current correlation reproduces the primary H2S viscosity data to within experimental uncertainty. The precision of the new correlation varies from reference quality (better than ± 0.20 %) at low-densities to an estimated ± 5 % at 100 MPa and temperatures between (373 and 423) K. Outside this range of temperature there are no data to validate the accuracy of the model at elevated pressures; therefore we have conservatively estimated an uncertainty of roughly 10 % in the low-temperature and high-density region (T < 323 K up to 100 MPa) and 5 % for the high-temperature region (T > 450 K up to 100 MPa).
    Journal of Chemical & Engineering Data 10/2012; 57(11):3014–3018. DOI:10.1021/je300601h · 2.05 Impact Factor
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    ABSTRACT: The rate coefficients for the reaction of 1,4-dioxane with atomic chlorine were measured from T = 292-360 K using the relative rate method. The reference reactant was isobutane and the experiments were made in argon with atomic chlorine produced by photolysis of small concentrations of Cl2. The rate coefficients were put on an absolute basis by using the published temperature dependence of the absolute rate coefficients for the reference reaction. The rate coefficients for the reaction of Cl with 1,4-dioxane were found to be independent of total pressure from p = 290 to 782 Torr. The experimentally measured rate coefficients showed a weak temperature dependence, given by k(exp)(T) = (8.4(-2.3)(+3.1)) × 10(-10) exp(-(470 ± 110)/(T/K)) cm3 molecule (-1) s(-1). The experimental results are rationalized in terms of statistical rate theory on the basis of molecular data obtained from quantum-chemical calculations. Molecular geometries and frequencies were obtained from MP2/aug-cc-pVDZ calculations, while single-point energies of the stationary points were computed at CCSD(T) level of theory. The calculations indicate that the reaction proceeds by an overall exothermic addition-elimination mechanism via two intermediates, where the rate-determining step is the initial barrier-less association reaction between the chlorine atom and the chair conformer of 1,4-dioxane. This is in contrast to the Br plus 1,4-dioxane reaction studied earlier, where the rate-determining step is a chair-to-boat conformational change of the bromine-dioxane adduct, which is necessary for this reaction to proceed. The remarkable difference in the kinetic behavior of the reactions of 1,4-dioxane with these two halogen atoms can be consistently explained by this change in the reaction mechanism.
    The Journal of Physical Chemistry A 05/2011; 115(20):5105-11. DOI:10.1021/jp201803g · 2.77 Impact Factor
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    ABSTRACT: The dissociation of 1, 2 and 4% 1,4-dioxane dilute in krypton was studied in a shock tube using laser schlieren densitometry, LS, for 1550-2100 K with 56 ± 4 and 123 ± 3 Torr. Products were identified by time-of-flight mass spectrometry, TOF-MS. 1,4-dioxane was found to initially dissociate via C-O bond fission followed by nearly equal contributions from pathways involving 2,6 H-atom transfers to either the O or C atom at the scission site. The 'linear' species thus formed (ethylene glycol vinyl ether and 2-ethoxyacetaldehyde) then dissociate by central fission at rates too fast to resolve. The radicals produced in this fission break down further to generate H, CH(3) and OH, driving a chain decomposition and subsequent exothermic recombination. High-level ab initio calculations were used to develop a potential energy surface for the dissociation. These results were incorporated into an 83 reaction mechanism used to simulate the LS profiles with excellent agreement. Simulations of the TOF-MS experiments were also performed with good agreement for consumption of 1,4-dioxane. Rate coefficients for the overall initial dissociation yielded k(123Torr) = (1.58 ± 0.50) × 10(59) × T(-13.63) × exp(-43970/T) s(-1) and k(58Torr) = (3.16 ± 1.10) × 10(79) × T(-19.13) × exp(-51326/T) s(-1) for 1600 < T < 2100 K.
    Physical Chemistry Chemical Physics 03/2011; 13(9):3686-700. DOI:10.1039/c0cp01541e · 4.20 Impact Factor
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    ABSTRACT: The kinetics of the unimolecular dissociation of propyne and allene, C3H4 + M → C3H3 + H + M, was investigated behind reflected shock waves at temperatures between 1400 and 2150 K and at pressures near 0.3, 1.3, 2.6 (propyne only), and 4.0 bar with argon as bath gas. Rate coefficients were obtained from the initial slope of the hydrogen-atom concentration–time profiles monitored with atomic resonance absorption spectroscopy at the Lyman α wavelength (121.6 nm). Within the experimental uncertainty (±30%), identical rate coefficients for propyne and allene decomposition were obtained, indicating a fast mutual isomerization. The dissociation reactions are shown to be in the low-pressure limit with a bimolecular rate coefficient . From a combination of our experimental results with kinetic data from the literature, we infer the following temperature and pressure dependence of the rate coefficient, which reproduces most of the experimental data at temperatures between 1200 and 2400 K and pressures between 0.1 and 5 bar better than within a factor of two: . This corresponds to a bimolecular rate coefficient in concentration units of .
    Proceedings of the Combustion Institute 01/2011; 33(1):267-272. DOI:10.1016/j.proci.2010.05.072 · 2.37 Impact Factor
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    ABSTRACT: The kinetic behaviour for the reaction of atomic bromine with tetrahydrofuran has been analysed using the information from quantum chemical calculations. Structures and energy profiles were first obtained using density functional theory (DFT) employing the Dunning’s basis sets of triple-zeta quality, and then for an accurate energetic description, single-point calculations were carried out at the coupled-cluster with single and double excitations (CCSD) and the fourth-order Møller–Plesset (MP4(SDQ)) levels of theory. The rate coefficients and the equilibrium constants for the potential reaction channels were obtained from the statistical rate theories and statistical thermodynamics, respectively, using the results of quantum chemical calculations; and the results were compared with our recently published experimental data. In terms of reaction mechanism, this reaction was found to be analogous to the reactions of the Br atom with 1,4-dioxane and with methanol, where the reaction proceeds via an addition–elimination mechanism. The dominant reaction channel involved coordination of the approaching Br atom to one of the hydrogen atoms adjacent to the ether oxygen atom, i.e., β-hydrogen abstraction is uncompetitive. Although the complexes formed by direct coordination of the Br atom to the ether oxygen atom appeared in the reaction mechanism, we were not able to link them specifically to any reaction. The density functional theory predicted an activation energy and enthalpy of reaction that were much smaller than the experimental values, which led to an overestimation of the theoretical rate coefficients. The source of this discrepancy could be attributed to the overbinding of the transition states and of the tetrahydrofuranyl radical by DFT. Single-point calculations at the DFT structures using the CCSD and MP4(SDQ) methods yielded an accurate energetic description of the reaction of tetrahydrofuran with bromine, resulting in rate coefficients that showed excellent agreement with the experimental values.
    Canadian Journal of Chemistry 11/2010; 88(11):1136-1145. DOI:10.1139/V10-092 · 1.01 Impact Factor
  • Binod R Giri, John M Roscoe
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    ABSTRACT: The reactions of Cl with tetrahydrofuran, tetrahydropyran, and dimethyl ether have been studied as a function of temperature, pressure, and O(2) concentration. The temperature was varied from approximately 280 to 360 K, the mole fraction of O(2) ranged from zero to approximately 0.6, and the experiments were made in a bath of argon at total pressures ranging from approximately 300 to 760 Torr. The rate coefficients were measured using the relative rate method with gas chromatographic analysis. The reaction of Cl with isobutane was the reference reaction, the rate coefficients for which were calibrated against the reaction of propane with chlorine atoms as a function of temperature. The rate coefficients were unaffected by the concentration of O(2) or by variation in pressure. The rate coefficient for the reaction of Cl with isobutane increased slightly with decreasing temperature. This weak temperature dependence of the rate coefficient was in satisfactory agreement with information in the literature and is represented in Arrhenius form by k(T) = (1.02(-0.25)(+0.32)) x 10(-10) exp(99 +/- 88/T) cm(3) molecule(-1) s(-1), where the uncertainties represent two standard deviations. The rate coefficients for the reactions of Cl with the ethers did not show a statistically significant dependence on temperature. Their average values over our range of temperature are: for Cl + tetrahydrofuran, k = (2.71 +/- 0.34) x 10(-10) cm(3) molecule(-1) s(-1); for Cl + tetrahydropyran, k = (2.03 +/- 0.82) x 10(-10) cm(3) molecule(-1) s(-1); and for Cl + dimethyl ether, k = (1.73 +/- 0.22) x 10(-10) cm(3) molecule(-1) s(-1), in which the uncertainties are again two standard deviations.
    The Journal of Physical Chemistry A 08/2010; 114(32):8369-75. DOI:10.1021/jp1037409 · 2.77 Impact Factor
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    ABSTRACT: A combination of experiment and theory is applied to the self-reaction kinetics of phenyl radicals. The dissociation of phenyl iodide is observed with both time-of-flight mass spectrometry, TOF-MS, and laser schlieren, LS, diagnostics coupled to a diaphragmless shock tube for temperatures ranging from 1276 to 1853 K. The LS experiments were performed at pressures of 22 +/- 2, 54 +/- 7, and 122 +/- 6 Torr, and the TOF-MS experiments were performed at pressures in the range 500-700 Torr. These observations are sensitive to both the dissociation of phenyl iodide and to the subsequent self-reaction of the phenyl radicals. The experimental observations indicate that both these reactions are more complicated than previously assumed. The phenyl iodide dissociation yields approximately 6% C(6)H(4) + HI in addition to the major and commonly assumed C(6)H(5) + I channel. The self-reaction of phenyl radicals does not proceed solely by recombination, but also through disproportionation to benzene + o-/m-/p-benzynes, with comparable rate coefficients for both. The various channels in the self-reaction of phenyl radicals are studied with ab initio transition state theory based master equation calculations. These calculations elucidate the complex nature of the C(6)H(5) self-reaction and are consistent with the experimental observations. The theoretical predictions are used as a guide in the development of a model for the phenyl iodide pyrolysis that accurately reproduces the observed laser schlieren profiles over the full range of the observations.
    The Journal of Physical Chemistry A 08/2010; 114(32):8240-61. DOI:10.1021/jp1031064 · 2.77 Impact Factor
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    ABSTRACT: The rate coefficient for the reaction of atomic bromine with 1,4-dioxane was measured from approximately 300 to 340 K using the relative rate method. Iso-octane and iso-butane were used as reference compounds, and the experiments were made in a bath of argon containing up to 210 Torr of O(2) at total pressures between 200 and 820 Torr. The rate coefficients were not affected by changes in pressure or O(2) concentration over our range of experimental conditions. The ratios of rate coefficients for the reaction of dioxane relative to the reference compound were put on an absolute basis by using the published absolute rate coefficients for the reference reactions. The variation of the experimentally determined rate coefficients with temperature for the reaction of Br with 1,4-dioxane can be given by k(1)(exp)(T) = (1.4 +/- 1.0) x 10(-11)exp[-23.0 +/- 1.8) kJ mol(-1)/(RT)] cm(3) molecule(-1) s(-1). We rationalized our experimental results in terms of transition state theory with molecular data from quantum chemical calculations. Molecular geometries and frequencies were obtained from MP2/aug-cc-pVDZ calculations, and single-point energies of the stationary points were obtained at CCSD(T)/CBS level of theory. The calculations indicate that the 1,4-dioxane + Br reaction proceeds in an overall endothermic addition-elimination mechanism via a number of intermediates. The rate-determining step is a chair-to-boat conformational change of the Br-dioxane adduct. The calculated rate coefficients, given by k(1)(calc)(T) = 5.6 x 10(-11)exp[-26.6 kJ mol(-1)/(RT)] cm(3) molecule(-1) s(-1), are in very good agreement with the experimental values. Comparison with results reported for the reactions of Br with other ethers suggests that this multistep mechanism differs significantly from that for abstraction of hydrogen from other ethers by atomic bromine.
    The Journal of Physical Chemistry A 10/2009; 114(1):291-8. DOI:10.1021/jp908168u · 2.77 Impact Factor
  • Binod Raj Giri, John M Roscoe
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    ABSTRACT: The rate coefficients for the reactions of atomic bromine with toluene, tetrahydrofuran, and tetrahydropyran were measured from approximately 295 to 362 K using the relative rate method. Iso-octane was used as the reference compound for the reaction with toluene, and iso-octane and toluene were used as the reference compounds for the reaction with tetrahydrofuran; tetrahydrofuran was used as the reference compound for the reaction with tetrahydropyran. The rate coefficients were found to be unaffected by changes in pressure and oxygen concentration. The rate coefficient ratios were converted to absolute values using the absolute rate coefficient for the reaction of Br with the reference compound. The absolute rate coefficients, in the units cm(3) molecule(-1) s(-1), for the reaction of Br with toluene are given by k(T) = (3.7 +/- 1.7) x 10(-12) exp(-(1.63 +/- 0.15) x 10(3)/T), for the reaction of Br with tetrahydrofuran by k(T) = (3.7 +/- 2.7) x 10(-10) exp(-(2.20 +/- 0.22) x 10(3)/T), and for the reaction of Br with tetrahydropyran by k(T) = (3.6 +/- 1.8) x 10(-10) exp(-(2.35 +/- 0.16) x 10(3)/T). The uncertainties represent one standard deviation. The Arrhenius parameters for these reactions are compared with results in the literature for dimethyl ether, diethyl ether, and a series of saturated hydrocarbons, and the effects of structural variation on these parameters are identified.
    The Journal of Physical Chemistry A 07/2009; 113(28):8001-10. DOI:10.1021/jp903293y · 2.77 Impact Factor
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    ABSTRACT: The reactions of hydrogen atoms with phenyl radicals, H + C(6)H(5) -> products (1). and with benzene, H + C(6)H(6) -> products (2), have been studied behind reflected shock waves in the temperature range 1200-1350 K with argon as the bath gas. H-atom resonance absorption spectrometry at 121.6 nm was used as detection technique. Hydrogen atoms and phenyl radicals were produced by thermal decomposition of C(2)H(5)I and C(6)H(5)I, respectively. Low initial concentrations (similar to 10(12)-10(15) cm(-3)) were employed to suppress consecutive bimolecular reactions as far as possible. The rate coefficients were determined from fits of the H atom concentration-time profiles, in terms of a small mechanism. For reaction (1), a temperature-independent rate coefficient k(1) = 1.3X10(-10) cm(3) s(-1) was obtained at pressures around 1.3 bar. For the rate coefficient of reaction (2), the temperature dependence can be expressed as k(2)(T) = 5.8X10(-10) exp(-8107 K/T) cm(3) s(-1). and a pressure dependence was not observed between 1.3 and 4.3 bar. The uncertainties of k(1) and k(2) were estimated to be +/- 40%.
    Zeitschrift für Physikalische Chemie 05/2009; 223(4-5):539-549. DOI:10.1524/zpch.2009.6036 · 1.18 Impact Factor
  • Binod Raj Giri, John M. Roscoe
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    ABSTRACT: The thermal dissociation of fluoroethane has been studied using shock tube (ST)/time-of-flight mass spectrometry (TOF-MS) at 500 and 1200 Torr over the temperature range 1200-1550 K. The ST/TOF-MS experiments confirm that elimination of HF is the only reaction channel and rate coefficients for this reaction were extracted from concentration/time profiles derived from the mass spectra. Results from a novel diaphragmless shock tube coupled to the TOF-MS are also presented and demonstrate the unique ability of this apparatus to generate sufficiently reproducible shock waves that signal averaging can be performed over multiple experiments; something that is not possible with a conventional shock tube. The dissociation is also studied with ab initio transition state theory based master equation simulations. A modest increase in the calculated barrier height (i.e., by 1 kcal mol(-1)) yields predicted high pressure rate coefficients that are in good agreement with the existing literature data. The present pressure dependent observations are accurately reproduced for a downwards energy transfer for neon at 1200 to 1500 K of approximately 270 cm(-1), which is somewhat smaller than that found in previous studies on fluorinated ethanes with the same bath gases.
    Physical Chemistry Chemical Physics 12/2008; 10(41):6266-73. DOI:10.1039/b808168a · 4.20 Impact Factor
  • Robert S. Tranter, Binod R. Giri
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    ABSTRACT: A novel, diaphragmless shock tube (DFST) has been developed for use in high temperature chemical kinetic studies. The design of the apparatus is presented along with performance data that demonstrate the range and reproducibility of reaction conditions that can be generated. The ability to obtain data in the fall off region, confined to much narrower pressure ranges than can be obtained with a conventional shock tube is shown, and results from laser schlieren densitometry experiments on the unimolecular dissociation of phenyl iodide ( P<sub>2</sub>=57±9 and 122±7  torr , T<sub>2</sub>=1250–1804  K ) are presented. These are compared with results similar to those that would be obtained from a classical shock tube and the implications for extrapolation by theoretical methods are discussed. Finally, the use of the DFST with an online mass spectrometer to create reproducible experiments that can be signal averaged to improve signal/noise and the quality of mass peaks is demonstrated; something that is not possible with a conventional shock tube where each experiment has to be considered unique.
    Review of Scientific Instruments 10/2008; 79(9-79):094103 - 094103-6. DOI:10.1063/1.2976671 · 1.58 Impact Factor
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    ABSTRACT: This paper reports measurements of the thermal dissociation of 1,1-difluoroethane in the shock tube. The experiments employ laser-schlieren measurements of rate for the dominant HF elimination using 10% 1,1-difluoroethane in Kr over 1500-2000 K and 43 < P < 424 torr. The vinyl fluoride product of this process then dissociates affecting the late observations. We thus include a laser schlieren study (1717-2332 K, 75 < P < 482 torr in 10 and 4% vinyl fluoride in Kr) of this dissociation. This latter work also includes a set of experiments using shock-tube time-of-flight mass spectrometry (4% vinyl fluoride in neon, 1500-1980 K, 500 < P < 1300 torr). These time-of-flight experiments confirm the theoretical expectation that the only reaction in vinyl fluoride is HF elimination. The dissociation experiments are augmented by laser schlieren measurements of vibrational relaxation (1-20% C(2)H(3)F in Kr, 415-1975 K, 5 < P < 50 torr, and 2 and 5% C(2)H(4)F(2) in Kr, 700-1350 K, 6 < P < 22 torr). These experiments exhibit very rapid relaxation, and incubation delays should be negligible in dissociation. An RRKM model of dissociation in 1,1-difluoroethane based on a G3B3 calculation of barrier and other properties fits the experiments but requires a very large DeltaE(down) of 1600 cm(-1), similar to that found in a previous examination of 1,1,1-trifluoroethane. Dissociation of vinyl fluoride is complicated by the presence of two parallel HF eliminations, both three-center and four-center. Structure calculations find nearly equal barriers for these, and TST calculations show almost identical k(infinity). An RRKM fit to the observed falloff again requires an unusually large DeltaE(down) and the experiments actually support a slightly reduced barrier. These large energy-transfer parameters now seem routine in these large fluorinated species. It is perhaps a surprising result for which there is as yet no explanation.
    Physical Chemistry Chemical Physics 08/2007; 9(31):4164-76. DOI:10.1039/b703124f · 4.20 Impact Factor
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    ABSTRACT: The kinetics of the reaction of hydrogen atoms with propyne (pC3H4) was experimentally studied in a shock tube at temperatures ranging from 1200 to 1400 K and pressures between 1.3 and 4.0 bar with Ar as the bath gas. The hydrogen atoms (initial mole fraction 0.5-2.0 ppm) were produced by pyrolysis of C2H5I and monitored by atomic resonance absorption spectrometry under pseudo-first-order conditions with respect to propyne (initial mole fraction 5-20 ppm). From the hydrogen atom time profiles, overall rate coefficients k(ov) identical with -([pC3H4][H])(-1) x d[H]/dt for the reaction H + pC3H4 --> products ( not equal H) were deduced; the following temperature dependence was obtained: kov = 1.2 x 10(-10) exp(-2270 K/T) cm(3) s(-1) with an estimated uncertainty of +/-20%. A pressure dependence was not observed. The results are analyzed in terms of statistical rate theory with molecular and transition state data from quantum chemical calculations. Geometries were optimized using density functional theory at the B3LYP/6-31G(d) level, and single-point energies were computed at the QCISD(T)/cc-pVTZ level of theory. It is confirmed that the reaction proceeds via an addition-elimination mechanism to yield C2H2 + CH3 and via a parallel direct abstraction to give C3H3 + H2. Furthermore, it is shown that a hydrogen atom catalyzed isomerization channel to allene (aC3H4), H + pC3H4 --> aC3H4 + H, is also important. Kinetic parameters to describe the channel branching of these reactions are deduced.
    The Journal of Physical Chemistry A 06/2007; 111(19):3812-8. DOI:10.1021/jp070833c · 2.78 Impact Factor
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    ABSTRACT: A shock tube (ST) with online, time-of-flight mass spectrometric (TOF-MS) detection has been constructed for the study of elementary reactions at high temperature. The ST and TOF-MS are coupled by a differentially pumped molecular beam sampling interface, which ensures that the samples entering the TOF-MS are not contaminated by gases drawn from the cold end wall thermal boundary layer in the ST. Additionally, the interface allows a large range of postshock pressures to be used in the shock tube while maintaining high vacuum in the TOF-MS. The apparatus and the details of the sampling system are described along with an analysis in which cooling of the sampled gases and minimization of thermal boundary layer effects are discussed. The accuracy of kinetic measurements made with the apparatus has been tested by investigating the thermal unimolecular dissociation of cyclohexene to ethylene and 1,3-butadiene, a well characterized reaction for which considerable literature data that are in good agreement exist. The experiments were performed at nominal reflected shock wave pressures of 600 and 1300 Torr, and temperatures ranging from 1260 to 1430 K. The rate coefficients obtained are compared with the earlier shock tube studies and are found to be in very good agreement. As expected no significant difference is observed in the rate constant between pressures of 600 and 1300 Torr.
    Review of Scientific Instruments 04/2007; 78(3):034101. DOI:10.1063/1.2437150 · 1.58 Impact Factor
  • Binod R Giri, Robert S Tranter
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    ABSTRACT: The dissociation of 1,1,1,-trifluoroethane, a potential non-RRKM reaction, has been studied at 600 and 1200 Torr and high temperatures (1500-1840 K) using a new shock tube/time-of-flight mass spectrometer (ST/TOF-MS). These data obtained by an independent method are in good agreement with the laser schlieren, LS, experiments of Kiefer et al. [J. Phys. Chem. A 2004, 108, 2443-2450] and extend the range of that experimental dataset. The data have been simulated by both standard RRKM calculations and the non-RRKM model reported by Kiefer et al. but with <DeltaE(down)> = 750 cm(-1). Both the RRKM and non-RRKM calculations provide equally good fits to the ST/TOF-MS data. Neither model simulates the combined ST/TOF-MS and LS datasets particularly well. However, the non-RRKM model predicts a pressure dependency closer to that observed in the experiments than the RRKM model.
    The Journal of Physical Chemistry A 04/2007; 111(9):1585-92. DOI:10.1021/jp066232n · 2.78 Impact Factor

Publication Stats

156 Citations
55.72 Total Impact Points

Institutions

  • 2012
    • The University of Calgary
      • Department of Chemistry
      Calgary, Alberta, Canada
  • 2009–2011
    • Acadia University
      • Department of Chemistry
      Wolfville, Nova Scotia, Canada
  • 2007–2011
    • Karlsruhe Institute of Technology
      • Institute of Physical Chemistry
      Carlsruhe, Baden-Württemberg, Germany
    • Argonne National Laboratory
      • Division of Chemical Sciences and Engineering
      Downers Grove, Illinois, United States