bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular beam scattering studies of the reaction D + H2 (v = 0) and D + H2 (v = 1) → HD + H
Authors: Goetting R. , Toennies J. P. , Vodegel M. 
Published: January 2005

AbstractThe reaction D + H2 → HD + H has been investigated in two molecular beam scattering experiments. Angular and time‐of‐flight distributions have been measured for the initial vibrational ground state (v = 0) at a most probable collision energy of Ecm = 1.5 eV and for the first vibrational excited state (v = 1) at Ecm = 0.28 eV with the same apparatus. Results for the ground‐state experiment are compared with quasiclassical trajectory calculations(QCT) on the LSTH‐hypersurface transformed into the laboratory system and averaged over the apparatus distributions. The agreement isquite satisfactory. At this high collision energy the HD products are no longer scattered in a backward direction but in a wide angular region concentrated about θ = 90° in the center‐of‐mass system. The absolute reactive cross section has been determined and the agreement with the theoretical value from QCT calculations is within the experimental error. The high sensitivity of the experiment to different properties of the doubly differential cross section has also been demonstrated. A preliminary evaluation of the experiment with initial vibrational excitation (v = 1) shows that the HD‐product molecules are preferably backward scattered and the change of internal energy is small supporting the concept of a reaction which is adiabatic with respect to the internal degrees of freedom.
A coupled states calculation of accurate quantum rate constants for H + H2
Authors: Colton Mitchell C. , Schatz George C. 
Published: January 2005

AbstractIn this article we present the results of converged quantum reactivescattering calculations of thermal rate constants for H + H2 using the Liu‐Siegbahn‐Truhlar‐Horowitz (LSTH) potential energy surface. These calculations are based on the coupled states (CS) approximation wherein rotational states having different body fixed angular momentum projection quantum numbers are decoupled. By comparision with accurate coupled channel results on the Porter‐Karplus No. 2 (PK2) potential surface, we estimate that the maximumerror in thermal rate constants arising from both this approximation and from other numerical approximations in the calculation is less than 25%. We also show that the sum over projection quantum numbers Ω associated with the CS calculation may be approximated quite accurately in terms of the Ω = 0 rate constants by assuming that the |Ω| > 0 rate constants differ from Ω = 0 by a shift in activation energy, which reflects the vibrationally adiabatic bending energy associated with each Ω.Comparison of the LSTH rate constants with experiment indicates average errors of 16% and 24% relative to the two modern measurementsof the rate constants for H + H2. These errors are reduced to 18% and 9% if the CS rate constants are multiplied by exp(0.0065 eV/kT). The expected error (based on recent quantum structure calculations) associated with the 0.425 eV barrier of theLSTH potential surface is 0.0065 eV. Overall, the agreement of either the LSTH or modified LSTH rate constants with experiment is within the 32% maximum disagreement between the two experimental measurements at all butthe lowest temperature that has been studied.Comparison of our CS rate constants with the results from simpler theories is considered using both the LSTH and PK2 potential surfaces. The best overall agreement is with transition state theories that use accurate dynamical methods to calculate tunnelling factors. These include reduced dimensionality quantum dynamics methods and variational transition state theory using either the Marcus‐Coltrin or least action ground‐state tunnelling paths. Comparison with the results of quasiclassical trajectory calculations indicates substantial errors at low temperatures.
Dynamical stereochemistry of the hydrogen exchange reaction: A computational study
Authors: Schechter I. , Levine R. D. 
Published: January 2005

AbstractThe barrier for the hydrogen exchange reaction increases with the bend angle of H3. The implications for the dynamics of the reaction are explored on two levels. The static one uses the concept of a relaxed potential. This provides for a convenient, yet realistic representation. Itallows for the response of the molecule to the approaching atom. Among features made very evident by the relaxed potential is the possibility that hotH atoms can react by insertion. It also shows the widening of the cone of acceptance upon reagent vibrational excitation. On the dynamical level, classical trajectory computations are used to illustrate the dependence of the reactivity on the angle of attack and on the translational and vibrational excitation of the reagents. Detailed product distributions are generally not sensitive to the attack angle. An exception is the HD/H2 branching ratio in H + HD reactive collisions.
Semiclassical variational transition state calculations for the reactions of H and D with thermal and vibrationally excited H2
Authors: Garrett Bruce C. , Truhlar Donald G. , Varandas A. J. C. , Blais Normand C. 
Published: January 2005

AbstractWe present calculations of the rate constants for the title reactions on a new accurate potential energy surface with a 9.65 kcal mol−1 barrier and a carefully fitted long‐range attraction. The low‐temperature thermal rate constant decreases from the previously calculated value, corresponding to a surface with a barrier of 9.80 kcal mol−1, which is opposite to the direction of change expectedbecause of the change in barrier height. This demonstrates the sensitivity of tunneling contributions to more global characteristics of the surface. The excited‐state (n = 1) rate constants alsochange slightly, but not nearly enough to settle the controversial disagreement of theory with experiment for these rate constants.
Kinetics of the reactions of halogenated methyl radicals (CF3, CF2Cl, CFCl2, and CCl3) with molecular chlorine
Authors: Timonen Raimo S. , Russell John J. , Gutman David 
Published: January 2005

AbstractThe kinetics of four gas‐phase reactions involving halogenated methyl radicals (R  CF3, CF2Cl, CFCI2, and CCI3) with molecular chlorine have been studied using a tubular reactor coupled to a photoionization mass spectrometer. The radicals were homogeneously generated by the pulsed photolysis of precursor molecules at 193 nm. The subsequent decays of the radical concentration were monitored in real‐time experiments as a function of Cl2 concentration to obtain the rate constants of these R + Cl2 reactions. Where possible, the rate constants were measured as a function of temperature to determine Arrhenius parameters. Apparent discrepancies between these measured rate constants for CF3 and CCl3 with Cl2 and ones obtained in prior indirect studies are explained. The higher activation energies for these R + Cl2 reactions compared to that of the CH3 + Cl2 reaction are attributed in part to the different polarities of the transition states formed.
Room temperature rate constants for the reaction of OH with selected chlorinated and oxygenated hydrocarbons
Authors: Edney E. O. , Kleindienst T. E. , Corse E. W. 
Published: January 2005

AbstractA study was conducted to measure the hydroxyl radical rate constants using a relative rate procedure in which the photolysis of methyl nitrite was the source of OH. During the course of this study, the OH rate constant was measured for a number of chlorinated solvents for which measurements have not previously been reported or for which there are few reliable measurements.Room temperature OH rate constants are presented for six chlorinated hydrocarbons (allyl chloride, benzyl chloride, chlorobenzene, epichlorohydrin, trichloroethylene, and vinylidene chloride) and four oxygenated hydrocarbons (acrolein, methacrolein, methyl ethyl ketone, and propylene oxide). Also included are OH rate constants for alkanes (ethane, propane, isobutane, and cyclohexane), alkenes (trans−2‐butene and isoprene), and aromatic hydrocarbons (benzene, toluene, o−, m−, and p‐xylene). Rate constants for compounds not previously reported include vinylidene chloride (1.49 ± 0.21 × 10−11 cm3 molecule−1 s−1) and benzyl chloride (2.96 ± 0.15 × 10−12 cm3 molecule−1 s−1). The analysis for chlorinated hydrocarbons included a correction for possible chlorine atom reactions.
The mechanism and rate parameters for the pyrolysis of n‐hexane in the range 723–823 K
Authors: Imbert Freddy E. , Marshall Roger M. 
Published: January 2005

AbstractThe pyrolysis of n‐hexane has been investigated in the ranges 723–823 K and 10–100 Torr at up to 3% decomposition. The reaction is homogeneous and free from the self‐inhibition by olefin products observed for several other alkanes. The products of the reaction are hydrogen, methane, ethane, ethene, propene, but‐1‐ene, and pent‐1‐ene, with smaller amounts of propane. It is shown that the results are in quantitative agreement with a conventional Rice‐Herzfeld chain mechanism terminated by the combination and disproportionation of ethyl radicals, but with the mechanism extended so as to include the unimolecular isomerizations via a six‐membered cyclic transition state between 1‐hexyl and 2‐hexyl (1‐methylpentyl) radicals.The overall rate constant of initiation is estimated to be given by

The rate constant for the reaction
equation image
is given by

which when combined with published data gives an Arrhenius plot curved upwards at low values of 1/T as has been observed for several other hydrogen abstraction reactions of methyl and of ethyl. Estimates are made of rate constants and ratios of rate constants for several reactions of the free radicals involved in the reaction. It is suggested that the minor product propane arises mainly from a hydrogen abstraction by 1‐propyl from hexane with a contribution from a minor termination process involving ethyl and methyl.
A critical review of the chemical kinetics of SF4, SF5, and S2F10 in the gas phase
Authors: Herron John T. 
Published: January 2005

AbstractThe gas phase chemical kinetics of SF4, SF5, and S2F10 are reviewed with particular emphasis on relevance to the general problem of the dielectric breakdown of SF6. Specific reaction systems treated are SF4 + F2, SF5 + SF5, and the pyrolysis of S2F10. Computer modeling calculations were carried out to arrive at the best estimates of rate parameters. Based on the results of these calculations, sets of recommended rate parameters are provided. The major discrepancies and problems in establishing the kinetic data base are described. Thermochemical consequences of different model calculations are given.
Bimolecular QRRK analysis of methyl radical reactions
Authors: Dean A. M. , Westmoreland P. R. 
Published: January 2005

AbstractReactions which proceed through energized adducts, including radical recombinations, insertions, and addition to unsaturates, frequently exhibit unusual kinetic behavior. The branching ratios among various product channels are often complex functions of both temperature and pressure. Four such reactions involving methyl radicals are analyzed by combining chemical activation distribution functions with QRRK methods to predict rate constants for each channel. These include three oxidation paths, CH3 + O, CH3 + O2, CH3 + OH, and the addition reaction CH3 + C2H2. These predictions are compared to experiments wherever possible; generally, the agreement is quite satisfactory. Analysis of the energetics of the various reaction channels, using parameters which are readily available, provides a convenient framework for prediction. Suggested rate constants for the various channels for the four reactions are given at three pressures, 20, 760, and 7600 Torr, for the temperature range 300–2500 K. The approach used here can easily be applied to other reactions.
Kinetics of the reactions of the hydroxyl radical with dimethyl ether and diethyl ether
Authors: Tully Frank P. , Droege August T. 
Published: January 2005

AbstractAbsolute rate coefficients for the reactions of the hydroxyl radical with dimethyl ether (k1) and diethyl ether (k2) were measured over the temperature range 295–442 K. The rate coefficient data, in the units cm3 molecule−1 s−1, were fitted to the Arrhenius equations k1 (T) = (1.04 ± 0.10) × 10−11 exp[−(739 ± 67 cal mol−1)/RT] and k2(T) = (9.13 ± 0.35) × 10−12 exp[+(228 ± 27 kcal mol−1)/RT], respectively, in which the stated error limits are 2σ values. Our results are compared with those of previous studies of hydrogen‐atom abstraction from saturated hydrocarbons by OH. Correlations between measured reaction‐rate coefficients and CH bond‐dissociation energies are discussed.
Kinetics of the gas‐phase reactions of NO3 radicals with a series of alkynes, haloalkenes, and α,β‐unsaturated aldehydes
Authors: Atkinson Roger , Aschmann Sara M. , Goodman Mark A. 
Published: January 2005

AbstractRate constants for the gas‐phase reactions of NO3 radicals with a series of alkynes, haloalkenes, and α,β‐unsaturated aldehydes have been determined at 298 ± 2 K using a relative rate technique. Using rate constants for the reactions of NO3 radicals with ethene and propene of (1.1 ± 0.5) × 10−16 cm3 molecule−1 s−1 and (7.5 ± 1.6) × 10−15 cm3 molecule−1 s−1, respectively, the following rate constants (in units of 10−16 cm3 molecule−1 s−1) were obtained: acetylene, ≤0.23; propyne, 0.94 ± 0.44; vinyl chloride, 2.3 ± 1.1; 1,1‐dichloroethene, 6.6 ± 3.1; cis‐1,2‐dichloroethene, 0.75 ± 0.35; trans‐1,2‐dichloroethene, 0.57 ± 0.27; trichloroethene, 1.5 ± 0.7; tetrachloroethene, <0.4; allyl chloride, 2.9 ± 1.3; acrolein, 5.9 ± 2.8; and crotonaldehyde, 41 ± 9. The atmospheric implications of these data are discussed.
Kinetics, mechanism, and stereochemistry of Diels‐Alder reactions of CN‐substituted ethenes with cyclohexa‐1, 3‐diene in the gas phase
Authors: Van Mele B. , Huybrechts G. 
Published: January 2005

AbstractThe kinetics of the Diels‐Alder additions of CH2 = CHCN, CH2 = C(CH3) CN, and cis‐ and trans‐CH3CH = CHCN to cyclohexa‐1, 3‐diene have been studied in the gas phase. The stereochemistry of these reactions is discussed. In terms of a biradical mechanism, a minimum value of 4.1 ± 0.8 kcal mol−1 for the stabilizing effect of a CN group vis‐à‐vis a methyl group is shown to fit the experimental activation energies.
Differential energy distributions in nonthermal systems: Model calculations and applications to 18F‐for‐F nuclear recoil substitutions in CH3CF3
Authors: Rogers E. B. , Tang Y.‐N. , Rodgers A. S. , Chui C. K. 
Published: January 2005

AbstractA general method has been developed for the determination of the differential energy distribution in nonthermally activated reacting systems. A series of known distributions and kinetic models has been used to test this method and to determine its efficacy. Application was then made to the kinetic data of energetic CH3CF2 18F formed by the substitution of F by 18F produced by nuclear recoil. The distribution obtained for this activated CH3CF2 18F is seen to be highly energetic with a median energy of 137.6 kcal mol−1 and with 33.1% of the molecules possessing energy in excess of 171 kcal mol−1. The shape of the calculated distribution suggests that there are two mechanisms for the formation of CH3CF2 18F from CH3CF3 and 18F, as well as that 62 kcal mol−1 is a lower limit to the kinetic energy needed by the 18F atom for this substitution to take place.
The pyrolysis of acetylene‐styrene mixtures between 450 and 550°C
Authors: Chanmugathas C. , Heicklen Julian 
Published: January 2005

AbstractThe pyrolysis of acetylene‐styrene mixtures has been studied from 450–550°C in a quartz reaction vessel in the absence and presence of O2 or NO. The rates of disappearance of reactants and formation of adducts are first‐order in each reactant. The major product is polymer, with the adducts accounting for about 2.5% and 6.2% of the styrene removed at 450 and 550°C, respectively. The acetylene‐to‐styrene removal ratio is about 27 independent of temperature. The adducts formed are methyl indene and 1,2‐dihydronaphthalene. These are about half‐suppressed in the presence of O2 or NO. The rate coefficients for reactant removal and adduct formation are:

where the activation energies are in kJ/mol and the uncertainties are one standard deviation. As the reaction proceeds, the methyl indene and 1,2‐dihydronaphthalene decompose, and indene and naphthalene are formed. In addition, an unidentified isomer of naphthalene is produced as an initial minor product, and it also decomposes as the reaction proceeds.
Kinetics of the permanganate oxidation of formic acid in aqueous solution
Authors: Monzó Isidro S. , Palou Juan , Peñalver Joaquín , Valero Rosa 
Published: January 2005

AbstractThe kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid at 30°C were examined by the spectrophotometric method. The chemical reaction 2MnO + 3HCOOH + 2H+ → 2MnO2 + 3CO2 + 4H2O, appears to proceed via several parallel reactions. The overall rate equation has been obtained by using statistical multilinear regression analysis of the 660 cases studied, and the presence in the rate equation of two new terms in relation to previous studies shows that both permanganate autocatalytic effects and acid media inhibition must be taken into account when the reaction proceeds at constant ionic strength.
Rate constants for hydrogen abstraction by resonance stabilized radicals in high temperature liquids
Authors: Manka M. J. , Brown R. L. , Stein S. E. 
Published: January 2005

AbstractBenzylic H‐atom abstraction rates by diphenylmethyl radicals from a series of donors were determined in nonpolar liquids at elevated temperatures. Relative rates were converted to absolute rates via available equilibrium constant data for the dimerization of diphenylmethyl radicals. Abstraction by diphenylmethyl from 1, 2, 3, 4‐tetrahydronaphthalene (tetralin) was studied over the temperature range 489–573 K. Its Arrhenius expression is 109.9±0.3 exp{−(10183 ± 373)/T} M−1 s−1. Abstraction from other donors was studied at 548 K. Rate constant values ranged from a low of 3.6 M−1 s−1 for toluene to a high of 3000 M−1 s−1 for 9, 10‐dihydroanthracene. Similar reactions with the fluorenyl radical were also studied. In this case, relative rates were converted to absolute rates with an equilibrium constant for fluorenyl dimerization determined from the observed homolysis rate of the dimer and an assumed recombination rate. In addition, forward and reverse rate measurements yielded the equilibrium constant for hydrogen transfer between fluorenyl and diphenylmethyl. At 548 K, fluorenyl is favored by a factor of 13 over diphenylmethyl.
Kinetics, mechanism, and stereochemistry of Diels‐Alder reactions of carbonyl‐substituted ethenes with cyclohexa‐1,3‐diene in the gas phase
Authors: Van Mele B. , Tybaert C. , Huybrechts G. 
Published: January 2005

AbstractThe kinetics of the Diels–Alder additions of CH2  CHCHO, CH2C(CH3)CHO, and CH2CHC(CH3)O to cyclohexa‐1,3‐diene (CHD) have been studied in the gas phase. The stereochemistry and the mechanism of these reactions are discussed. In contrast with other Diels–Alder additions involving CHD as diene, a biradical mechanism does not fit the experimental results.
Rate constant for the reaction of OH radicals with dimethyl sulfide
Authors: Hsu Yen‐Chung , Chen Dze‐Shu , Lee Yuan‐Pern 
Published: January 2005

AbstractThe rate constants of the gas phase reaction of OH radicals with dimethyl sulfide (CH3SCH3) over the temperature range 260–393 K have been studied using the discharge flow‐resonance fluorescence technique. The rate constants were fitted by the Arrhenius equation k = (11.8 ± 2.2) × 10−12 exp[−(236 ± 150)/T] cm3 molecule−1 s−1 with k = (5.5 ± 1.0) × 10−12 cm3 molecule−1 s−1 at 298 K. Our results are in good agreement with the lower range of values reported previously. The observation of a small positive activation energy agrees well with that reported by Hynes et al. The rate constant was not affected by the total pressure variation (0.8–3.0 torr) or by the addition of oxygen (up to 1 torr) in the flow tube.
Pyrolysis of 2‐butyne/vinylacetylene mixtures between 350 and 450°C
Authors: Harper Charles , Heicklen Julian 
Published: January 2005

AbstractVinylacetylene and 2‐butyne mixtures were pyrolyzed at 350–450°C in the absence and presence of O2 and NO. The major product of the reaction is a polymer, but o‐xylene is also produced and was studied as the species of interest. The C8H10 formation rate is first‐order in C4H4 and C4H6. The rate coefficient is best fitted by

though it is not inconsistent with

where R is the ideal gas constant in kJ/mol‐K. O‐xylene formation occurs by two processes: a concerted molecular mechanism (⋍67%) and a singlet diradical mechanism (⋍33%).
The gas phase reactions of hydroxyl radicals with a series of aliphatic ethers over the temperature range 240–440 K
Authors: Wallington Timothy J. , Liu Renzhang , Dagaut Philippe , Kurylo Michael J. 
Published: January 2005

AbstractAbsolute rate constants were determined for the gas phase reactions of OH radicals with a series of linear aliphatic ethers using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for dimethylether (k1), diethylether (k2), and dipropylether (k3) were used to derive the Arrhenius expressions

and

At 296 K, the measured rate constants (in units of 10−13 cm3 molecule−1 s−1) were: k1 = (24.9 ± 2.2), k2 = (136 ± 9), and k3 = (180 ± 22). Room temperature rate constants for the OH reactions with several other aliphatic ethers were also measured. These were (in the above units): di‐n‐butylether, (278 ± 36); di‐n‐pentylether, (347 ± 20); ethyleneoxide, (0.95 ± 0.05); propyleneoxide, (4.95 ± 0.52); and tetrahydrofuran, (178 ± 16). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data.
Acuchem: A computer program for modeling complex chemical reaction systems
Authors: Braun Walter , Herron John T. , Kahaner David K. 
Published: January 2005

AbstractAcuchem is a program for solving the system of differential equations describing the temporal behavior of spatially homogeneous, isothermal, multicomponent chemical reaction systems. It is designed to provide modelers, data evaluators, and laboratory scientists with an easy to use program for modeling complex chemical reactions, and for presenting the results in tabular or graphical form. The program is described and some examples of its application given. Acuchem is designed to operate on the IBM Personal Computer family and other compatible microcomputers, and is available in a compiled version on a floppy disk.
Kinetics of hydroxyl radical reactions with formaldehyde and 1,3,5‐trioxane between 290 and 600 K
Authors: Zabarnick S. , Fleming J. W. , Lin M. C. 
Published: January 2005

AbstractAbsolute rate constants are measured for the reactions: OH + CH2O, over the temperature range 296–576 K and for OH + 1,3,5‐trioxane over the range 292–597 K. The technique employed is laser photolysis of H2O2 or HNO3 to produce OH, and laser‐induced fluorescence to directly monitor the relative OH concentration. The results fit the following Arrhenius equations: k (CH2O) = (1.66 ± 0.20) × 10−11 exp[−(170 ± 80)/RT] cm3 s−1 and k(1,3,5‐trioxane) = (1.36 ± 0.20) × 10−11 exp[−(460 ± 100)/RT] cm3 s−1. The transition‐state theory is employed to model the OH + CH2O reaction and extrapolate into the combustion regime. The calculated result covering 300 to 2500 K can be represented by the equation: k(CH2O) = 1.2 × 10−18 T2.46 exp(970/RT) cm3 s−1. An estimate of 91 ± 2 kcal/mol is obtained for the first CH bond in 1,3,5‐trioxane by using a correlation of CH bond strength with measured activation energies.