High-temperature Rate Constants Research Articles

High-temperature rate constants for CH3OCOH + OH reactions: the effects of multiple structures and paths

High-temperature rate constants for CH3OCOH + OH reactions: the effects of multiple structures and paths

High-Temperature Rate Constants for the Reaction of Hydrogen Atoms with Tetramethoxysilane and Reactivity Analogies between Silanes and Oxygenated Hydrocarbons.

The shock-tube technique has been used to investigate the H-abstraction reaction H + Si(OCH3)4 → H2 + Si(OCH2)(OCH3)3 behind reflected shock waves. C2H5I was used as a thermal in situ source for H atoms. The experiments covered a temperature range of 1111-1238 K, and pressures of 1.3-1.4 bar. H atom concentrations were monitored with atomic resonance absorption spectrometry (ARAS). Fits to the temporal H atom concentration profiles based on a developed chemical kinetics reaction mechanism were used for determining bimolecular rate constants. Experimental total H-abstraction rate constants were well represented by the Arrhenius equation ktotal( T) = 10-9.16±0.24 exp(-25.5 ± 5.6 kJ mol-1/ RT) cm3 s-1. Transition state theory (TST) calculations based on the G4 level of theory show excellent agreement with experimentally obtained rate constants, i.e., the theory values of k( T) deviate by less than 25% from the experimental results. Regarding H abstractions, we have compared the reactivity of C-H bonds in Si(OCH3)4 with the reactivity of C-H bonds in dimethyl ether (CH3OCH3). Present experimental and theoretical results indicate that at high temperatures, i.e., T > 500 K, CH3OCH3 is a good reactivity analog to Si(OCH3)4, i.e., kH+Si(OCH3)4( T) ∼ 1.5 × kH+CH3OCH3( T). On the basis of these results, we discuss the possibility of drawing reactivity analogies between oxygenated silanes and oxygenated hydrocarbons.

Tunneling Reaction Kinetics for the Hydrogen Abstraction Reaction H + H2S → H2 + HS in the Interstellar Medium.

The hydrogen abstraction reaction between H and H2S, yielding HS and H2 as products, has been studied within the framework of interstellar surface chemistry. High-temperature rate constants below 2000 K are calculated in the gas phase and are in agreement with previously reported values. Subsequently, low-temperature rate constants down to 55 K are presented for the first time that are of interest to astrochemistry, i.e., covering both bimolecular and unimolecular reaction mechanisms. For this, a so-called implicit surface model is used. In strict terms, this is a structural gas-phase model in which the restriction of the rotation in the solid state is taken into account. The calculated kinetic isotope effects are explained in terms of the difference in activation and delocalization. All rate constants are calculated at the UCCSD(T)-F12/cc-VTZ-F12 level of theory. Finally, we show that the energetics of the reaction is affected to an only small extent by the presence of H2O or H2S molecular clusters that simulate an ice surface, calculated at the MPWB1K/def2-TZVP level of theory.

Site-specific reaction rate constant measurements for various secondary and tertiary H-abstraction by OH radicals

Reaction rate constants for nine site-specific hydrogen atom (H) abstraction by hydroxyl radicals (OH) have been determined using experimental measurements of the rate constants of Alkane+OH→Products reactions. Seven secondary (S20, S21, S22, S30, S31, S32, and S33) and two tertiary (T100 and T101) site-specific rate constants, where the subscripts refer to the number of carbon atoms (C) connected to the next–nearest–neighbor (N–N–N) C atom, were obtained for a wide temperature range (250–1450K). This was done by measuring the reaction rate constants for H abstraction by OH from a series of carefully selected large branched alkanes. The rate constant of OH with four different alkanes, namely 2,2-dimethyl-pentane, 2,4-dimethyl-pentane, 2,2,4-trimethyl-pentane (iso-octane), and 2,2,4,4-tetramethyl-pentane were measured at high temperatures (822–1367K) using a shock tube and OH absorption diagnostic. Hydroxyl radicals were detected using the narrow-line-width ring-dye laser absorption of the R1(5) transition of OH spectrum near 306.69nm.Previous low-temperature rate constant measurements are added to the current data to generate three-parameter rate expressions that successfully represent the available direct measurements over a wide temperature range (250–1450K). Similarly, literature values of the low-temperature rate constants for the reaction of OH with seven normal and branched alkanes are combined with the recently measured high-temperature rate constants from our group [1]. Subsequent to that, site-specific rate constants for abstractions from various types of secondary and tertiary H atoms by OH radicals are derived and have the following modified Arrhenius expressions:S20=8.49×10-17T1.52exp(73.4K/T)cm3molecule-1s-1(250–1450K)S21=1.07×10-15T1.07exp(208.3K/T)cm3molecule-1s-1(296–1440K)S22=2.88×10-13T0.41exp(-291.5K/T)cm3molecule-1s-1(272–1311K)S30=3.35×10-18T1.97exp(323.1K/T)cm3molecule-1s-1(250–1366K)S31=1.60×10-18T2.0exp(500.0K/T)cm3molecule-1s-1(250–1351K)S32=9.65×10-17T1.45exp(180.0K/T)cm3molecule-1s-1(297–1367K)S33=2.83×10-19T2.25exp(501.3K/T)cm3molecule-1s-1(250–1365K)T100=5.69×10-16T1.32exp(76.8K/T)cm3molecule-1s-1(297–1375K)T101=1.05×10-16T1.38exp(577.9K/T)cm3molecule-1s-1(297–1362K)

Direct Measurements of Rate Constants for the Reactions of CH3 Radicals with C2H6, C2H4, and C2H2 at High Temperatures

The shock tube technique has been used to study the reactions CH3 + C2H6 → C2H4 + CH4 + H (1), CH3 + C2H4 → Products + H (2), and CH3 + C2H2 → Products + H (3). Biacetyl, (CH3CO)2, was used as a clean high temperature thermal source for CH3-radicals for all the three reactions studied in this work. For reaction 1, the experiments span a T-range of 1153 K ≤ T ≤ 1297 K, at P ~ 0.4 bar. The experiments on reaction 2 cover a T-range of 1176 K ≤ T ≤ 1366 K, at P ~ 1.0 bar, and those on reaction 3 a T-range of 1127 K ≤ T ≤ 1346 K, at P ~ 1.0 bar. Reflected shock tube experiments performed on reactions 1-3, monitored the formation of H-atoms with H-atom Atomic Resonance Absorption Spectrometric (ARAS). Fits to the H-atom temporal profiles using an assembled kinetics model were used to make determinations for k1, k2, and k3. In the case of C2H6, the measurements of [H]-atoms were used to derive direct high-temperature rate constants, k1, that can be represented by the Arrhenius equation k1(T) = 5.41 × 10(-12) exp(-6043 K/T) cm(3) molecules(-1) s(-1) (1153 K ≤ T ≤ 1297 K) for the only bimolecular process that occurs, H-atom abstraction. TST calculations based on ab initio properties calculated at the CCSD(T)/CBS//M06-2X/cc-pVTZ level of theory show excellent agreement, within ±20%, of the measured rate constants. For the reaction of CH3 with C2H4, the present rate constant results, k2', refer to the sum of rate constants, k(2b) + k(2c), from two competing processes, addition-elimination, and the direct abstraction CH3 + C2H4 → C3H6 + H (2b) and CH3 + C2H4 → C2H2 + H + CH4 (2c). Experimental rate constants for k2' can be represented by the Arrhenius equation k2'(T) = 2.18 × 10(-10) exp(-11830 K/T) cm(3) molecules(-1) s(-1) (1176 K ≤ T ≤ 1366 K). The present results are in excellent agreement with recent theoretical predictions. The present study provides the only direct measurement for the high-temperature rate constants for these channels. Lastly, measurements of H-atoms from the reaction of CH3 with C2H2 provided direct unambiguous determinations of the rate constant for the dominant process under the present experimental conditions, the addition-elimination, CH3 + C2H2 → p-C3H4 + H (3b). Experimental rate constants for k(3b) can be represented by the Arrhenius equation k(3b)(T) = 5.16 × 10(-13) exp(-3852 K/T) cm(3) molecules(-1) s(-1) (1127 K ≤ T ≤ 1346 K). The present determinations for k(3b) represent the only direct measurements for this reaction and are also in good agreement with recent theoretical predictions. The present experimental k(3b) values were also used to derive rate constants, k(-3b), for the more extensively studied back-process, the reaction of H-atoms with propyne. The best fit Arrhenius equation, combining the presently derived k(-3b) values with a recent experimental determination for k(-3b), can be represented by k(-3b)(T) = 3.87 × 10(-11) exp(-1313 K/T) cm(3) molecules(-1) s(-1) (870 K ≤ T ≤ 1346 K). The present studies represent a novel implementation of the sensitive H-ARAS technique to measure rate constants for poorly characterized and difficult to isolate "slow" CH3-radical reactions with stable C2 hydrocarbons.

High temperature rate constants for H/D + methyl formate and methyl acetate

The reactions of D/H with methyl formate (MF) and methyl acetate (MA) have been studied with both shock-tube experiments and ab initio transition state theoretical calculations. D-atom profiles were measured behind reflected shock waves using D-atom atomic resonance absorption spectrometry (ARAS) over the temperature range 1050–1270K, at pressures ≅0.5atm.The title reactions have been theoretically studied at the CCSD(T)/cc-pv∞z//MP2/aug-cc-pvtz and CCSD(T)/cc-pv∞z//B3LYP/6-311++G(d,p) levels of theory. Theoretical calculations suggest the dominance of the abstraction processes in comparison to addition processes in the 300–2000K T-range. Over the T-range of the present experiments, the theoretically predicted isotope effects, kD/kH, are near unity.D-atom depletion in the present experiments is sensitive only to the reactions,(A)D+CH3OC(O)H→products(B)D+CH3OC(O)CH3→productsSimulations of the measured D-atom profiles allow for determinations of total rate constants for the processes (A) and (B). In combination with results obtained from recent H-ARAS experiments from our laboratory on MF decomposition, total experimental rate constants kA can be described by the Arrhenius equation,kA=(4.47±1.54)×10-10exp(-5843±416K/T)cm3molecule-1s-1(1050–1270K)For H/D+MF, total experimental rate constants, kA, and branching ratios agree well with theoretical predictions.For D/H+MA, total rate constants predicted by theory are in reasonable agreement with the experimental data. The theoretical predictions are preferred for use, with kB represented by the modified Arrhenius equation,kB=3.078×10-19T2.78exp(-3261K/T)cm3molecule-1s-1(500–2000K)To our knowledge, the present experiments are the first direct measurements for the title reactions and the rate constants from this combined experimental/theoretical effort are recommended for use in combustion modeling.

Direct measurements of the high temperature rate constants of the reactions NCN + O, NCN + NCN, and NCN + M

The rate constant of the reaction NCN + O has been directly measured for the first time. According to the revised Fenimore mechanism, which is initiated by the NCN forming reaction CH + N(2)→ NCN + H, this reaction plays a key role for prompt NO(x) formation in flames. NCN radicals and O atoms have been quantitatively generated by the pyrolysis of NCN(3) and N(2)O, respectively. NCN concentration-time profiles have been monitored behind shock waves using narrow-bandwidth laser absorption at a wavelength of λ = 329.1302 nm. Whereas no pressure dependence was discernible at pressures between 709 mbar < p < 1861 mbar, a barely significant temperature dependence corresponding to an activation energy of 5.8 ± 6.0 kJ mol(-1) was found. Overall, at temperatures of 1826 K < T < 2783 K, the rate constant can be expressed as k(NCN + O) = 9.6 × 10(13)× exp(-5.8 kJ mol(-1)/RT) cm(3) mol(-1) s(-1) (±40%). As a requirement for accurate high temperature rate constant measurements, a consistent NCN background mechanism has been derived from pyrolysis experiments of pure NCN(3)/Ar gas mixtures, beforehand. Presumably, the bimolecular secondary reaction NCN + NCN yields CN radicals hence triggering a chain reaction cycle that efficiently removes NCN. A temperature independent value of k(NCN + NCN) = (3.7 ± 1.5) × 10(12) cm(3) mol(-1) s(-1) has been determined from measurements at pressures ranging from 143 mbar to 1884 mbar and temperatures ranging from 966 K to 1900 K. At higher temperatures, the unimolecular decomposition of NCN, NCN + M → C + N(2) + M, prevails. Measurements at temperatures of 2012 K < T < 3248 K and at total pressures of 703 mbar < p < 2204 mbar reveal a unimolecular decomposition close to its low pressure limit. The corresponding rate constants can be expressed as k(NCN + M) = 8.9 × 10(14)× exp(-260 kJ mol(-1)/RT) cm(3) mol(-1) s(-1)(±20%).

Direct Measurements of the Rate Constants of the Reactions NCN + NO and NCN + NO2 Behind Shock Waves

The high-temperature rate constants of the reactions NCN + NO and NCN + NO(2) have been directly measured behind shock waves under pseudo-first-order conditions. NCN has been generated by the pyrolysis of cyanogen azide (NCN(3)) and quantitatively detected by sensitive difference amplification laser absorption spectroscopy at a wavelength of 329.1302 nm. The NCN(3) decomposition initially yields electronically excited (1)NCN radicals, which are subsequently transformed to the triplet ground state by collision-induced intersystem crossing (CIISC). CIISC efficiencies were found to increase in the order of Ar < NO(2) < NO as the collision gases. The rate constants of the NCN + NO/NO(2) reactions can be expressed as k(NCN+NO)/(cm(3) mol(-1)s(-1)) = 1.9 × 10(12) exp[-26.3 (kJ/mol)/RT] (±7%,ΔE(a) = ± 1.6 kJ/mol, 764 K < T < 1944 K) and k(NCN+NO(2))/(cm(3) mol(-1)s(-1)) = 4.7 × 10(12) exp[-38.0(kJ/mol)/RT] (±19%,ΔE(a) = ± 3.8 kJ/mol, 704 K < T < 1659 K). In striking contrast to reported low-temperature measurements, which are dominated by recombination processes, both reaction rates show a positive temperature dependence and are independent of the total density (1.7 × 10(-6) mol/cm(3) < ρ < 7.6 × 10(-6) mol/cm(3)). For both reactions, the minima of the total rate constants occur at temperatures below 700 K, showing that, at combustion-relevant temperatures, the overall reactions are dominated by direct or indirect abstraction pathways according to NCN + NO → CN + N(2)O and NCN + NO(2) → NCNO + NO.

An improved H 2/O 2 mechanism based on recent shock tube/laser absorption measurements

An updated H 2/O 2 reaction mechanism is presented that incorporates recent reaction rate determinations in shock tubes from our laboratory. These experiments used UV and IR laser absorption to monitor species time-histories and have resulted in improved high-temperature rate constants for the following reactions: H + O 2 = OH + O H 2 O 2 ( + M ) = 2 OH ( + M ) OH + H 2 O 2 = HO 2 + H 2 O O 2 + H 2 O = OH + HO 2 The updated mechanism also takes advantage of the results of other recent rate coefficient studies, and incorporates the most current thermochemical data for OH and HO 2. The mechanism is tested (and its performance compared to that of other H 2/O 2 mechanisms) against recently reported OH and H 2O concentration time-histories in various H 2/O 2 systems, such as H 2 oxidation, H 2O 2 decomposition, and shock-heated H 2O/O 2 mixtures. In addition, the mechanism is validated against a wide range of standard H 2/O 2 kinetic targets, including ignition delay times, flow reactor species time-histories, laminar flame speeds, and burner-stabilized flame structures. This validation indicates that the updated mechanism should perform reliably over a range of reactant concentrations, stoichiometries, pressures, and temperatures from 950 to greater than 3000 K.

Kinetics of the Gas-Phase Reaction of OH with Chlorobenzene

The kinetics of the reaction of hydroxyl radicals with chlorobenzene was studied experimentally using a pulsed laser photolysis/pulsed laser induced fluorescence technique over a wide range of temperatures, 298-670 K, and at pressures between 13.33 and 39.92 kPa. The bimolecular rate constants demonstrate different behavior at low and high temperatures. At room temperature, T = 298.8 +/- 1.5 K, the rate constant is equal to (6.02 +/- 0.34) x 10(-13) cm3 molecule(-1) s(-1); at high temperatures (474-670 K), the rate constant values are significantly lower and have a positive temperature dependence that can be described by an Arrhenius expression k1(T) = (1.01 +/- 0.35) x 10(-11) exp[(-2490 +/- 170 K)/T] cm3 molecule(-1) s(-1). This behavior is consistent with the low-temperature reaction being dominated by reversible addition and the high-temperature reaction representing abstraction and addition-elimination channels. The potential energy surface of the reaction was studied using quantum chemical methods, and a transition state theory model was developed for all reaction channels. The temperature dependences of the high-temperature rate constants obtained in calculations using the method of isodesmic reactions for transition states (IRTS) and the CBS-QB3 method are in very good agreement with experiment, with deviations smaller than the estimated experimental uncertainties. The G3//B3LYP-based calculated rate constants are in disagreement with the experimental values. The IRTS-based model was used to provide modified Arrhenius expressions for the temperature dependences of the rate constant for the abstraction and addition-elimination (Cl replacement) channels of the reaction.

Shock tube measurements of high temperature rate constants for OH with cycloalkanes and methylcycloalkanes

High temperature experiments were performed with the reflected shock tube technique using multi-pass absorption spectrometric detection of OH radicals at 308 nm. The present experiments span a wide T-range, 801–1347 K, and represent the first direct measurements of the title rate constants at T > 500 K for cyclopentane and cyclohexane and the only high temperature measurements for the corresponding methyl derivatives. The present work utilized 48 optical passes corresponding to a total path length ∼4.2 m. As a result of this increased path length, the high [OH] detection sensitivity permitted unambiguous analyses for measuring the title rate constants. The experimental rate constants in units, cm 3 molecule −1 s −1, can be expressed in Arrhenius form as k OH + Cyclopentane = ( 1.90 ± 0.30 ) × 10 − 10 exp ( − 1705 ± 156 K / T ) ( 813–1341 K ) , k OH + Cyclohexane = ( 1.86 ± 0.24 ) × 10 − 10 exp ( − 1513 ± 123 K / T ) ( 801–1347 K ) , k OH + Methylcyclopentane = ( 2.02 ± 0.19 ) × 10 − 10 exp ( − 1799 ± 96 K / T ) ( 859–1344 K ) , k OH + Methylcyclohexane = ( 2.55 ± 0.30 ) × 10 − 10 exp ( − 1824 ± 114 K / T ) ( 836–1273 K ) . These results and lower- T experimental data were used to obtain three parameter evaluations of the experimental rate constants for the title reactions over an even wider T-range. These experimental three parameter fits to the rate constants in units, cm 3 molecule −1 s −1, are k OH + Cyclopentane = 1.390 × 10 − 16 T 1.779 exp ( 97 K / T ) cm 3 molecule − 1 s − 1 ( 209–1341 K ) , k OH + Cyclohexane = 3.169 × 10 − 16 T 1.679 exp ( 119 K / T ) cm 3 molecule − 1 s − 1 ( 225–1347 K ) , k OH + Methylcyclopentane = 6.903 × 10 − 18 T 2.148 exp ( 536 K / T ) cm 3 molecule − 1 s − 1 ( 296–1344 K ) , k OH + Methylcyclohexane = 2.341 × 10 − 18 T 2.325 exp ( 602 K / T ) cm 3 molecule − 1 s − 1 ( 296–1273 K ) . High level electronic structure methods were used to characterize the first three reactions in order to provide reliable extrapolations of the rate constants from 250–2000 K. The results of the theoretical predictions for OH + cyclohexane and OH + methylcyclopentane were sufficient to make a theoretical prediction for OH + methylcyclohexane. The present recommended rate expressions for OH with cyclohexane, and methylcyclohexane, give rate constants that are 15–25% higher (over the T-range 800–1300 K) than the rate constants utilized in recent modeling efforts aimed at addressing the oxidation of cyclohexane and methylcyclohexane. The current measurements reduce the uncertainties in rate constants for the primary cycloalkane consumption channel in a high temperature oxidation environment.

High temperature rate constants for OH+ alkanes

Rate constants for H-atom abstractions by OH radicals from a series of alkanes (propane, n-butane, i-butane and neo-pentane) have been measured at high temperatures with the reflected shock tube technique using multi-pass absorption spectrometric detection of OH radicals at 308nm. The experiments represent the first direct measurements of these rate constants at T>1000K and span a wide T-range, 797–1259K.The present work utilized 80 optical passes corresponding to a total path length of ∼7m. As a result of this increased path length, the high [OH] detection sensitivity permitted pseudo-first-order analysis for unambiguously measuring the total rate constants. The experimental rate constants can be represented in Arrhenius form as,kC3H8+OH=6.671×10-11exp(-1543K/T)cm3molecule-1s-1(797–1248K)kn-C4H10+OH=9.674×10-11exp(-1569K/T)cm3molecule-1s-1(800–1236K)ki-C4H10+OH=9.114×10-11exp(-1654K/T)cm3molecule-1s-1(846–1221K)kneo-C5H12+OH=1.060×10-10exp(-1947K/T)cm3molecule-1s-1(841–1259K)The present results have been combined with prior lower-T measurements to generate three-parameter rate expressions that adequately represent the available direct measurements (within 25%) over a wide temperature regime (250–1250K). High-level ab-initio electronic structure theory computations of the molecular properties of reactants, products and transition states have been used to estimate theoretical rate constants with conventional transition state theory (CTST). The theoretical rate constants are excellent representations of the available experimental data (deviations less than 25%) and thereby offer a reliable method for extrapolation to higher-T as well as for extracting branching ratios for primary, secondary and tertiary abstractions.

Wide temperature range (T = 295 K and 770–1305 K) study of the kinetics of the reactions HCO + NO and HCO + NO2 using frequency modulation spectroscopy

The rate constants for , HCO + NO --> HNO + CO, and , HCO + NO(2)--> products, have been measured at temperatures between 770 K < T < 1305 K behind reflected shock waves and, for the purpose of a consistency check, in a slow flow reactor at room temperature. HCO radicals were generated by 193 nm excimer laser photolysis of diluted gas mixtures containing glyoxal, (CHO)(2), and NO or NO(2) in argon and were monitored using frequency modulation (FM) absorption spectroscopy. Kinetic simulations based on a comprehensive reaction mechanism showed that the rate constants for the title reactions could be sensitively extracted from the measured HCO profiles. The determined high temperature rate constants are k(1)(769-1307 K) = (7.1 +/- 2.7) x 10(12) cm(3) mol(-1) s(-1) and k(2)(804-1186 K) = (3.3 +/- 1.8) x 10(13) cm(3) mol(-1) s(-1). The room temperature values were found to be in very good agreement with existing literature data and show that both reactions are essentially temperature independent. The weak temperature dependence of can be explained by the interplay of a dominating direct abstraction pathway and a complex-forming mechanism. Both pathways yield the products HNO + CO. In contrast to , no evidence for a significant contribution of a direct high temperature abstraction channel was found for . Here, the observed temperature independent overall rate constant can be described by a complex-forming mechanism with several product channels. Detailed information on the strongly temperature dependent channel branching ratios is provided. Moreover, the high temperature rate constant of , OH + (CHO)(2), has been determined to be k(7) approximately 1.1 x 10(13) cm(3) mol(-1) s(-1).

Reflected shock tube studies of high-temperature rate constants for OH + C2H2 and OH + C2H4

The reflected shock tube technique with multi-pass absorption spectrometric detection of OH-radicals at 308 nm (corresponding to a total path length of approximately 4.9 m) has been used to study the reactions, OH + C(2)H(2)--> products (1) and OH + C(2)H(4)--> C(2)H(3) + H(2)O (2). The present optical configuration gives a S/N ratio of approximately 1 at approximately 0.5-1.0 x 10(12) radicals cm(-3). Hence, kinetics experiments could be performed at [OH](0) = approximately 4-20 ppm thereby minimizing secondary reactions. OH was produced rapidly from the dissociations of either CH(3)OH or NH(2)OH (hydroxylamine). A mechanism was then used to obtain profile fits that agreed with the experiment to within <+/-5%. The derived Arrhenius expressions, in units of cm(3) molecule(-1) s(-1) are: k(1) = (1.03 +/- 0.24) x 10(-10) exp(-7212 +/- 417 K/T) for 1509-2362 K and k(2) = (10.2 +/- 5.8) x 10(-10) exp(-7411 +/- 871 K/T) for 1463-1931 K. The present study is the first ever direct measurement for reaction (1) at temperatures >1275 K while the present results extend the temperature range for (2) by approximately 700 K. These values are compared with earlier determinations and with recent theoretical calculations. The calculations agree with the present data for both reactions to within +/-10% over the entire T-range.

REMOVED: Initiation in CH 4/O 2: High temperature rate constants for CH 4+O 2 → CH 3+HO 2

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy .

Simulation of the Double Proton Transfer Dynamics in the Benzoic Acid Dimer

A numerical simulation of the rate constants of the double proton transfer in the benzoic acid dimer at partial and complete deuteration of hydrogen bonds in the dimer as well as at different hydrostatic pressures applied to the sample has been carried out on the basis of the model of a multistage process activated by equilibrium radiation. It has been shown that this model, as opposed to the known approach based on the synthesis of two processes — activation (Boltzmann–Arrhenius model) and molecular tunneling (Goldanskii model) — can describe both low- and high-temperature rate constants of reactions using a single set of parameters characterizing the process of interaction of the transforming molecule with the thermal field.

Direct measurements of the reaction H + CH2O → H2+ HCO behind shock waves by means of Vis–UV detection of formaldehyde

AbstractThe combination of sensitive detection of formaldehyde by 174 nm absorption and use of ethyl iodide as a hydrogen atom source allowed direct measurements of the reaction H + CH2O → H2+ HCO behind shock waves. The rate constant was determined for temperatures from 1510 to 1960 K to bek2= 6.6 × 1014exp(−40.6 kJ mol−1/RT) cm3mol−1s−1(Δ logk2= ± 0.22)Considering the low uncertainty ink2, which accounts both for experimental and mechanism‐induced contributions, this result supports the upper range of previously reported, largely scattered high temperature rate constants. Vis–UV light of 174 nm was generated by a microwave N2discharge lamp. At typical reflected shock wave conditions of 1750 K and 1.3 atm, as low as 33 ppm formaldehyde could be detected. High temperature absorption cross sections of CH2O and other selected species have been determined. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 374–386, 2002

Computational chemistry and aeroassisted orbital transfer vehicles

An analysis of the radiative heating phenomena encountered during a typical aeroassisted orbital transfer vehicle (AOTV) trajectory was made to determine the potential impact of computational chemistry on AOTV design technology. Both equilibrium and nonequilibrium radiation mechanisms were considered. This analysis showed that computational chemistry can be used to predict (1) radiative intensity factors and spectroscopic data; (2) the excitation rates of both atoms and molecules; (3) high-temperature reaction rate constants for metathesis and charge exchange reactions; (4) particle ionization and neutralization rates and cross sections; and (5) spectral line widths.

Measurement of high temperature rate constants using a discharge flow shock tube

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMeasurement of high temperature rate constants using a discharge flow shock tubeG. P. Glass and R. B. QuyCite this: J. Phys. Chem. 1979, 83, 1, 30–33Publication Date (Print):January 1, 1979Publication History Published online1 May 2002Published inissue 1 January 1979https://doi.org/10.1021/j100464a005RIGHTS & PERMISSIONSArticle Views42Altmetric-Citations10LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (562 KB) Get e-Alerts

Shock tube study of carbon disulfide oxidation

The induction zone of shock-initiated explosions of carbon disulfide-oxygen-argon mixtures was studied using the reflected wave end-on method. Profiles of chemiluminescence at 490 nm, attributed to SO2o, and infrared emission at 5 μm, attributed to CS2 and CO, were analyzed to deterrine the characteristic branched-chain growth rates and ignition delay times over the temperature range 1400–2100 K for CS2:O2 ratios varying from 1:9 to 3:10 with various dilutions in argon. Computer modelling in terms of a conventional mechanisms for the CS2−O2 reaction was able to account for the ignition delay times under a variety of assumptions about the high temperature rate constants, but no adjustments of the mechanism or the rate constants were found that were capable of giving satisfactorily correct models of the qualitative forms of the visible emission profiles or the mixture dependence of the growth rates.