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Showing papers on "Elementary reaction published in 1987"


Journal ArticleDOI
TL;DR: In this article, a systematically reduced four-step mechanism is proposed to provide the essential properties of methane-air diffusion flames such as the structure and extinction limits in a way similar to a full kinetic mechanism.

274 citations



Journal ArticleDOI
TL;DR: In this article, the process of bimolecular reaction between A and B is given by Eq. (1), taking into account the diffusion step bringing the two reactions in proximity.
Abstract: Chemical reactions require that at least two molecules or reacting groups come into close proximity so that energy, electrical charge, or chemical groups may be exchanged between them. The process of bimolecular reaction between A and B is given by Eq. (1), taking into account the diffusion step bringing the two reactions in proximity, (AB)

118 citations


Journal ArticleDOI
TL;DR: In this article, the kinetics of hydroisomerization and hydrocracking of n-octane, n-decane and n-dodecane were studied on a Pt/US-Y zeolite at 130 − 250°C, 5 − 100 bar total pressure and molar hydrogen to hydrocarbon ratios from 10 to 150.

81 citations


Journal ArticleDOI
TL;DR: In this article, the reaction kinetics of O3(v) in discharged O2/Ar mixtures at ∼1 Torr and 80-150 K were studied, and the effective "quasinascent" state distribution in recombination was also inferred.
Abstract: Spectrally resolved infrared chemiluminescence from vibrationally excited ozone, O3(v), has been used to study the reaction kinetics of O3(v) in discharged O2/Ar mixtures at ∼1 Torr and 80–150 K. Dependences of the excited state number densities on temperature and O2 mole fraction indicate O3(v) is formed primarily by three‐body recombination of O with O2 and is destroyed by rapid chemical reaction with O. Several secondary excitation reactions involving vibrationally and electronically excited O2 are also indicated. The data are treated with a detailed steady‐state analysis of the discharge kinetics, to extract estimates for rate coefficients of the key elementary reactions. The effective ‘‘quasinascent’’ state distribution in recombination is also inferred; this distribution shows selective recombination into the asymmetric stretching mode, but an apparently statistical (i.e., collisionally scrambled) behavior among the vibrational states within that mode. The results are discussed in terms of the detai...

79 citations


Journal ArticleDOI
TL;DR: In this article, it is shown that the production of state and internal energy-selected molecular ions is now possible by resonance-enhanced multi-photon ionization, and the metastable decay of these ions with sharp energy distribution can be observed and the decay rate constants have been measured with special techniques.

50 citations


Journal ArticleDOI
TL;DR: The non-Markovian theory of activated rate processes developed by Carmeli and Nitzan is applied to investigate unimolecular reactions in condensed phases with particular emphasis on the molecular size dependence of the effect of solvent friction on the reaction rate.
Abstract: The non‐Markovian theory of activated rate processes developed by Carmeli and Nitzan is applied to investigate unimolecular reactions in condensed phases with particular emphasis on the molecular size (number of internal degrees of freedom) dependence of the effect of solvent friction on the reaction rate. The model consists of one reaction coordinate coupled to n−1 nonreactive modes. The molecule solvent interaction is treated within the context of the generalized Langevin equation. The reaction dynamics may be roughly described as two consecutive processes: the well (energy diffusion) dynamics where it is assumed that fast intramolecular vibrational relaxation and slower overall molecular energy diffusion dominate the process, and the barrier dynamics where it is assumed that the motion along the reaction coordinate is only weakly coupled to the nonreactive modes. This model leads to a result for the reaction rate which, as in the one‐dimensional case, is obtained as the inverse of the sum of two times:...

40 citations


Journal ArticleDOI
TL;DR: In this paper, the reaction of F+ketene and F(2P)+ketene with fluoromethyl radicals was studied in a flow reactor and the reaction was identified as a major product of the F +ketene elementary reaction.
Abstract: The reactions of F(2P)+ketene and F(2P)+ketene‐d2 were studied in a flow reactor. Spectra of the radical products CH2F, CD2F, CH, CF, and atomic carbon were detected between 292–395 nm by resonance enhanced multiphoton ionization (REMPI) mass spectrometry. Fluoromethyl radicals were identified as a major product of the F+ketene elementary reaction. REMPI spectra of fluoromethyl radicals originated from two‐photon preparation of 3p, 4p, and 5p Rydberg states (quantum defect ∼0.6). Absorption of a third laser photon ionized the radicals, a 2+1 REMPI mechanism. Rydberg band origins were observed in CH2F at ν00=52 863, 63 275, and 67 265 cm−1 and in CD2F at ν00=52 786, 63 195, and 67 186 cm−1. A normal mode analysis revealed the vibrational frequencies of the C–F stretch, CH2 scissors, and out‐of‐plane bending modes in the Rydberg states. The ground state out‐of‐plane bending frequency in CH2F is 260(30) cm−1 and in CD2F it is 170(30) cm−1. CH radicals were generated by the photolysis of ketene and observed a...

37 citations


Journal ArticleDOI
TL;DR: In this paper, the reaction rate constant expressions k8 = 5.0 × 1014 exp(−60 kJ/RT) cm3 mol−1 s−1 for C22 + OH → CH2CO + H, k9 = 2.7 ×1014 exp (−63 kJ)/RT cm3 m mol− 1 s− 1 for C2H2+OH → C2O + H2O, and k18 = 2

33 citations


Journal ArticleDOI
01 Jan 1987
TL;DR: In this article, a discharge-flow system at 298 K was used to generate HS radicals for kinetic investigations, and the rate constant k(1) was obtained from the rate of H2S consumption under the condition [H2S] << [F]0======¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Abstract: The reaction of H2S with atomic fluorine (1) has been studied in a discharge-flow system at 298 K to generate HS radicals for kinetic investigations. Mass spectrometric detection with single ion counting was employed. The rate constant k(1) was obtained from the rate of H2S consumption under the condition [H2S] << [F]0 It has been shown that the reaction (1) provides a clean source of HS radicals. From the disappearance of HS radicals upon addition of reactants and the formation of products rate constants for the following reactions have been determined: The reaction of HS with O2 was also studied but it is too slow at room temperature to be followed with the present set up.

33 citations


Journal ArticleDOI
TL;DR: In this article, the authors consider the product-forming step as taking place in solid solution, and show that depending on the rigidities of the product molecule and of the parent crystal structure there may or may not occur, subsequently, crystallization of a product in its own structure.

Journal ArticleDOI
TL;DR: In this article, a simple gaseous reaction model involving 11 elementary reactions for 10 chemical species is proposed for silane and disilane pyrolyses at 550-750 K.
Abstract: A simple gaseous reaction model involving 11 elementary reactions for 10 chemical species is proposed for silane and disilane pyrolyses at 550–750 K; its appropriateness is examined by a calculation based on an one-dimensional nonsteady condition which includes gaseous reactions, diffusional transport and radical adsorptions The calculated results show that the model can successfully explain the experimental behavior of a gas composition concerning the time lag of hydrogen molecule production as well as the temperature and pressure dependences of the saturated higher silane concentrations The reaction model is applied to a SiH4–H2–N2 system; it predicts that dilution with hydrogen or the premixing of ca 4% of disilane is useful for obtaining a spatially uniform deposition rate in a flow-type CVD reactor

Journal ArticleDOI
01 Jul 1987
TL;DR: In this article, the rate constant for the reaction (1) CH3O + O products at 298 K has been determined using 248 nm laser co-photolysis of CH3ONO/O3 mixtures for the generation of CH 3O radicals and O atoms combined with LTF for time resolved detection of CH and product OH.
Abstract: The rate constant for the reaction (1) CH3O + O products at 298 K has been determined using 248 nm laser co-photolysis of CH3ONO/O3 mixtures for the generation of CH3O radicals and O atoms combined with LTF for time resolved detection of CH3O and product OH. k1 is found to be (2.5±0.7) 10−11 cm3/s with a relative yield of OH of Φ = -Δ[OH]/Δ[CH3O] = 0.12+0.08−0.04. The results are shown to be consistent with a primary capture mechanism on an electronically adiabatic surface forming highly vibrationally excited CH3O and followed by rapid subsequent decomposition or isomerization, viz. . From modelling of the OH yield using RRKM theory the isomerization barrier between CH3O2 and CH2OOH is placed near 160 kJ/mol in good agreement with recent ab initio calculations. As a consequence the CH3 + O2 combustion reaction is predicted to proceed primarily via the low energy CH2O + OH channel, in contrast to most previous suggestions.

Journal ArticleDOI
TL;DR: In this paper, the authors consider reaction paths for two prototypical chemical reactions: Li + HF, an electron-transfer reaction, and OH + H2, an abstraction reaction.
Abstract: The concept of a reaction path which continuously describes the transformation of reactants to products is firmly embedded in the lore of chemistry. A formal definition of the reaction path for a general molecular system was proposed by Fukui in 1970 as the path of steepest descent in mass-weighted cartesian coordinates from the transition state to reactants in one direction and to products in the other. In 1980 Miller, Handy and Adams advanced a formal theory of reaction dynamics based on harmonic fluctuations about the reaction path. We report reaction paths for two prototypical chemical reactions: Li + HF, an electron-transfer reaction, and OH + H2, an abstraction reaction. In the first we consider the connection between the energetic terms in the reactions path Hamiltonian and the electronic changes which occur upon reaction. In the second reaction we consider the treatment of vibrational effects in chemical reactions in the reaction-path formalism.

Journal ArticleDOI
TL;DR: In this paper, a procedure is described which allows one to deduce from flash photolysis data (absorbance change vs time) recorded at different temperatures the natural rate constants for the elementary reaction steps and the transient absorption spectra of the intermediates within a given kinetic scheme.
Abstract: A procedure is described which allows one to deduce from flash photolysis data (absorbance change vs time) recorded at different temperatures the natural rate constants for the elementary reaction steps and the transient absorption spectra of the intermediates within a given kinetic scheme. The selected solutions fulfil two requirements: (i) the rate constants for different temperatures follow Arrhenius’law; (ii) the absorption spectra of the intermediates are independent of temperature. The method is applied to the photocycle of bacteriorhodopsin; the selected model comprises two L-species, a branching at the M-intermediate directly back to BR and an equilibrium between M and O.

Journal ArticleDOI
TL;DR: In this paper, the rate coefficient of the reaction CN + O 2 → NCO + O (R3) was varied to match the measured and calculated concentration profiles, and the determined rate coefficient was found to be in good agreement with the result reported by Louge and Hanson in Int. J. Kin. 16: k 3 = 4.9 × 10 12 cm 3 mol -1 s -1

Journal ArticleDOI
TL;DR: The overall catalyzed reaction of isobutyraldehyde and oxygen consists of an initial burst followed by a steady state phase and the keto-enol equilibrium constant which is unaffected by phosphate which therefore acts as a true catalyst.

Journal ArticleDOI
01 Jul 1987-Polymer
TL;DR: In this article, the time-dependent changes in monomers, dimers, end reactive groups and central links occurring in the synthesis of polysulphone derived from dichlorodiphenylsuloxide and the sodium salt of diphenylolpropane in dilute solution in dimethylsulphoxide were investigated by nuclear magnetic resonance spectroscopy.

Journal ArticleDOI
TL;DR: In this paper, the authors compare the reaction F + Na2→ NaF + Na(i) in the thermal and hyperthermal regimes and see evidence of a transition from near-statistical to deterministic regime; the increased collision energy has narrowed the range of intermediate configurations.
Abstract: Comparing the reaction F + Na2→ NaF + Na(i)(where i are electronically excited states) in the thermal and hyperthermal regimes one sees evidence of a transition from near-statistical to a deterministic regime; the increased collision energy has narrowed the range of intermediate configurations. Ordering can be achieved more precisely by photoinducing reaction in an aligned condition, either in a van der Waals cluster (Wittig et al.) or in surface-aligned photoreaction. Both methods are reviewed. In the latter case the alignment can be demonstrated by studying photofragment angular distributions. The surface can enhance the photodissociation cross-section by 103–104 times. Theory indicates that reaction product angular distribution relative to the surface will be sensitive to the geometry of reactant adsorption. Photodetachment from surfaces could be used in a crossed ablated beam (CAB) variant of the crossed molecular-beam approach, employing beams which are purely free radicals, or (by ‘photoejection’) accelerated molecules. An adsorbate-covered surface with rectangular grooves that align photoreagents would constitute a ‘morphological catalyst’. We note pitfalls and progress in the realm of transition-state spectroscopy. Emission from sodium iodide vapour in the process of photodissociation, i.e. in an unbound ‘transition state’ NaI+, is obscured by the small fraction of NaI* that is present in a shallow bound state. For the case of H + D2→ HD + D it has proved possible to detect HD2[graphic omitted] in the transition state by two-photon ionization.

Journal ArticleDOI
TL;DR: In this paper, experimental and theoretical studies concerning the reaction kinetics of the solid state polymerization in diacetylene crystals are reported. But the authors do not consider the effect of the mismatch of the oligomer molecules in the crystal matrix.
Abstract: We report on experimental and theoretical studies concerning the reaction kinetics of the solid state polymerization in diacetylene crystals. The individual reaction steps of the short‐chain reaction intermediates (dimer, trimer, tetramer, ...) have been investigated by time resolved ESR and optical spectroscopy. In a microscopic theory energy barriers of molecular translations and rotations as well as the mismatch of the oligomer molecules in the crystal matrix are taken into account. The ‘‘molecular‐mechanical’’ model gained in this way is successful in describing the experimentally observed dependencies of the activation energy of the addition reaction on chain length, temperature, and conversion. It also explains the time‐conversion behavior of the reaction. Moreover, we gain information about the activation energy of the total reaction and can anticipate the temperature dependency of the chain length.

Journal ArticleDOI
01 Jul 1987
TL;DR: In this article, the scavenging efficiencies for different radicals were determined and measured as a function of the gas phase radical concentration, the flow of scavenger molecules, the pressure in the vacuum chamber, and the conditions of the discharge and the flow through the sampling nozzle.
Abstract: H and O atoms and methyl radicals produced in microwave discharges of H2/He, O2/He and CH4/He mixtures, respectively, were scavenged by supersonic nozzle probing with subsequent freezing and reaction with dimethyl disulfide on a liquid nitrogen cooled wall. The main reaction products for the three kinds of radicals were CH3SH, CH3S(O)SCH3 and CH3SCH3, respectively. Side products were CH3SCH2SSCH3 and CH3SSSCH3 for H atoms and CH3S(O)2SCH3 for O atoms. – The scavenging efficiencies for the different radicals were determined and measured as a function of the gas phase radical concentration, the flow of scavenger molecules, the pressure in the vacuum chamber, and the conditions of the discharge and the flow through the sampling nozzle. It is concluded that this method is suitable for light radicals with reservations in the case of H atoms and can probably be used with still better success for heavier radicals.

Journal ArticleDOI
01 Jul 1987
TL;DR: In this paper, a method of detecting radicals from low-pressure gas-phase systems by scavenging with dimethyl disulfide (DMD) has been applied to microwave discharges in C2H2/He mixtures.
Abstract: The method of detecting radicals from low-pressure gas-phase systems by scavenging with dimethyl disulfide (DMD) has been applied to microwave discharges in C2H2/He mixtures and to a C2H2/O2 flame. It was accomplished by condensing a supersonic nozzle beam from the reaction system together with a beam of DMD on a liquid-N2 cooled surface. The scavenging products were measured by GC/MS after warming-up. Radicals measured in the discharge were C2H, C4H, C6H, C3H2, C2 besides H atoms. Preliminary measurements on the flame showed that C6H5 (phenyl), CH2, C3H2, besides H and O atoms were prominent radicals at the end of the oxidation zone. The concentration of phenyl is of the same order as that of e.g. naphthalene. The method provides a means to distinguish condensible flame products from those that are formed during the sampling process when no scavenger is added.

01 Jan 1987
TL;DR: The DDHL model has been used in the engineering design of new thermal de NOx installation as discussed by the authors and has been shown to accurately predict the performance of the process in any given practical application.
Abstract: In 1972 the author, then with Exxon Research and Eng. Co. (ERE), discovered a new chemical reaction, the gas phase homogeneous reduction of NO to N2 and H20 by NH3, in the presence of O2. This reaction was both rapid and highly selective, i.e. with reaction times of 0.1 sec or less NO could be nearly quantitatively reduced by equimolar amounts of NH3 in the presence of O2 concentrations orders of magnitude greater than the NO. The discovery of this reaction made possible a new and remarkably simple method of controlling the emissions of NOx from stationary sources such as utility boilers and industrial process furnaces, the Thermal DeNOx process. To date this process has had upwards of 60 commercial applications and in recent instances NO reductions in excess of 90% have been achieved. One factor which helped make this success possible was the development of a predictive kinetic model, i.e. a model which described the kinetics of the reaction in terms of elementary reaction rate constants and which could be used to accurately predict the performance of the process in any given practical application. The model is routinely used in the engineering design of new Thermal DeNOx installation. Tomore » the author's knowledge this is the first instance in which a model based on elementary reaction rate constants has been so used. This success was the culmination of the efforts of workers both within and outside of ERE but this success has received less attention than it might have otherwise. Several papers and meeting presentations have outlined the general nature of the model, but the actual model itself has been disclosed only in one somewhat obscure patent. In this review the DDHL model will be discussed and compared with models published by others.« less

Journal ArticleDOI
01 Aug 1987
TL;DR: In this article, triplet anthraquinone (TQ) was used for the photochemical decomposition of α-phenylethyl hydroperoxide (HROOH) in the presence of air-saturated benzene and chlorobenzene.
Abstract: The quantum yields of the formation of products as well as their temperature dependence during the photochemical decomposition of α-phenylethyl hydroperoxide (HROOH) have been measured in the presence of triplet anthraquinone (TQ) in air-saturated benzene and chlorobenzene at 301–373 K. The photochemical and thermal decomposition of HROOH have been compared. Experimental results and their mathematical simulation indicate that in the reaction of TQ with HROOH peroxy radicals, HRO2, are generated. According to the measurements at T = 30 K, and the energy of activation of the reaction is about 5.9 kJ mol−1.


Journal ArticleDOI
TL;DR: In this article, a mechanistic kinetic model for the kinetics of grafting in solution polymerization is developed, which allows prediction of the rate of polymerization and grafting efficiency under various reaction conditions.
Abstract: A mechanistic kinetic model, which includes several elementary reactions occurring simultaneously, is developed for the kinetics of grafting in solution polymerization. This model allows prediction of the rate of polymerization and grafting efficiency under various reaction conditions. It also permits evaluation of grafting reaction rate constants. Experimental data available in the literature are used to test the model. Very good agreement is observed between the data and model predictions.

Book ChapterDOI
01 Jan 1987
TL;DR: The chapter discusses that for the chain-initiation reaction, the dissociation of hydrogen in bimolecular collisions has been considered in the past and appears plausible because it gave an explanation for the marked dependence of the rate of water formation on the partial pressure of hydrogen.
Abstract: This chapter discusses the thermal reaction between hydrogen and oxygen. There are many possible elementary reactions in the hydrogen-oxygen system, but their relative importance changes radically over diverse ranges of experimental variables. As conditions are altered, some reactions become insignificant while others come to the fore. The reaction mechanism is, therefore, circumscribed by the range of experimental conditions to which it applies. The chapter discusses that for the chain-initiation reaction, the dissociation of hydrogen in bimolecular collisions has been considered in the past. On the face of it, this reaction appeared plausible because it gave an explanation for the marked dependence of the rate of water formation on the partial pressure of hydrogen, and it appeared consistent with the observed overall activation energy in excess of 100 kcal. As neither the dissociation of hydrogen or of oxygen nor the gas-phase reaction between them can be admitted as the chain-initiation reaction, attention is focused on the experimentally established presence of H 2 O 2 in the reacting mixture. If H 2 O 2 is both formed and destroyed in a chain reaction, it attains a steady state concentration that is independent of the chain carrier concentration.

Journal ArticleDOI
TL;DR: In this article, the kinetics of radical polymerization of tetrafunctional monomers with intramolecular cyclization has been studied in the pre-gel stage by the Monte Carlo method.
Abstract: The kinetics of radical polymerization of tetrafunctional monomers with intramolecular cyclization has been studied in the pre-gel stage by the Monte Carlo method. The reaction was modelled on a body-centered cubic lattice using a unit cell with periodic boundary conditions; initiation, propagation, and cyclization (by two mechanisms) were considered as elementary reaction steps. Intramolecular cyclization by termination has been shown to influence substantially the reaction kinetics. The fraction of pendant double bonds remains constant during the reaction, in a qualitative agreement with experimental observations. The intramolecular cyclization has been found to play an important role in the investigated systems.

Book
01 Jan 1987
TL;DR: A previous workshop on modelling of chemical reaction systems held in 1980 was an attempt to find a common language of mathematicians, chemists, and engineers working in this interdisciplinary area.
Abstract: Chemical reaction systems of practical interest are usually very complex: They consist of a large number of elementary reactions (hundreds or thou sands in a small system), mostly with rate coefficients differing by many orders of magnitude, which leads to serious stiffness, and they are often coupled with surface reaction steps and convective or diffusive processes. Thus, the derivation of a "true" chemical mechanism can be extremely cumbersome. In most cases this is done by setting up "reaction models" which are improved step by step using, for example, perturbation theory, numerical simulation and sensitivity analysis (and - hopefully, in the near future - parameter identification procedures), and by comparison with experimental data on sensitive properties. Because of the complexity of these processes, it was very difficult in the past to convince engineers to apply methods using detailed mecha nisms given in terms of elementary reactions, and even in basic sciences there was scepticism about this ambitious aim. A previous workshop on modelling of chemical reaction systems held in 1980 was an attempt to find a common language of mathematicians, chemists, and engineers working in this interdisciplinary area. Since then considerable progress has been made by the simultaneous development of applied mathematics, an enor mous increase of computer capacity, and the development of experimental techniques in physical chemistry that have made available well-working reaction mechanisms in some fields of reaction kinetics."

Journal ArticleDOI
01 Oct 1987
TL;DR: In this article, the vibrational and rotational distributions for infrared chemiluminescence from F atoms with CH3I and CH2I2 in a fast flow apparatus under low pressure were determined for different nozzle configurations and changing reagent flows.
Abstract: Infrared chemiluminescence from HF is observed from the reactions of F atoms with CH3I and CH2I2 in a fast flow apparatus under low pressure. The vibrational and rotational distributions for HF are determined for different nozzle configurations and changing reagent flows. The vibrational distributions for v = 1 – 3 are interpreted by proposing two microscopic channels for HF product formation in both reaction systems.