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Elementary reaction

About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.


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Journal ArticleDOI
01 Jan 2000
TL;DR: In this article, a benzene supercritical water oxidation (SCWO) mechanism, based on published low-pressure benzene combustion mechanisms and submechanisms describing the oxidation of key intarmediates, was developed and analyzed to determine the controlling reactions under SCWO conditions of 750-860 K, 139-278 bar, and equivalence ratios from 0.5 to 2.5.
Abstract: A benzene supercritical water oxidation (SCWO) mechanism, based on published low-pressure benzene combustion mechanisms and submechanisms describing the oxidation of key intarmediates, was developed and analyzed to determine the controlling reactions under SCWO conditions of 750–860 K, 139–278 bar, and equivalence ratios from 0.5 to 2.5. To adapt the combustion mechanims to the lower temperature ( 220 bar) conditions, new reaction pathways were added, and quantum Rice-Ramsperger-Kassel theory was used to calculate the rate coefficients and, hence, product selectivities for pressure-dependent reactions. The most important difference between the benzene oxidation mechanism for supercritical water conditions and those for combustion conditions is reactions in supercritical water involving C 6 H 5 OO predicted to be formed by C 6 H 5 reacting with O 2 . Through the adjustment of the rate coefficients of two thermal decomposition pathways of C 6 H 5 OO, whose values are unknown, the model accurately predicts the measured benzene and phenol concentration profiles at 813 K, 246 bar, stoichiometric oxygen, and 3–7 s residence time and reproduces the finding that the carbon dioxide concentration exceeds that of carbon monoxide at all reaction conditions and levels of benzene conversion. Comparison of the model predictions to benzene SCWO data measured at several different conditions reveals that the model qualitatively explains the trends of the data and gives good quantitative agreement without further adjustment of rate coefficients.

28 citations

Journal ArticleDOI
TL;DR: In this article, the chemical reaction mechanism in solution is analyzed by using the Chemical Reaction Molecular Dynamics (CRMD) method where a solute molecule and a few solvent molecules are regarded as a supermolecule and the reaction dynamics can be analyzed in a time-dependent way on the intrasupermolecular potential surface.
Abstract: The chemical reaction mechanism in solution is analyzed by using the chemical reaction molecular dynamics (CRMD) method where a solute molecule and a few solvent molecules are regarded as a supermolecule and the chemical reaction dynamics can be analyzed in a time-dependent way on the intrasupermolecular potential surface. We have examined a proton transfer reaction, the formamidine-water system, and focused on the dynamic effect in the chemical reaction after considering the static «electronic» solvent effect. Two schemes, the constant-temperature scheme (CTS) and the constant-energy scheme (CES), have been employed, and a new type of critical state, named the dynamic transition state (DTS), was found by the appearance of a cusp in the hydrogen-bonding correlation function (HBCF). The cusp is due to the stopping of change in the O-H bond length, which produces a water molecule in the product region. In the CES, alternately modulated oscillation appeared, which is a characteristic in triatomic systems and should play an important role in energy flow in solution

28 citations

Journal ArticleDOI
TL;DR: A theoretical modeling of the reaction mechanism and kinetics in the gas- and aqueous phase was performed by using the unrestricted density functional theory with the BB1K functional, unrestricted coupled cluster UCCSD(T) method, and improved canonical variational theory.
Abstract: A pulse radiolysis study was carried out of the reaction rate constants and kinetic isotope effects of hydroxyl-radical-induced H/D abstraction from the most-simple α-amino acid glycine in its anionic form in water. The rate constants and yields of three predominantly formed radical products, glycyl (NH2–˙CH–CO2−), aminomethyl (NH2–˙CH2), and aminyl (˙NH–CH2–CO2−) radicals, as well as of their partially or fully deuterated analogs, were found to be of comparable magnitude. The primary, secondary, and primary/secondary H/D kinetic isotope effects on the rate constants were determined with respect to each of the three radicals. The unusual variety of products for such an elementary reaction between two small and simple species indicates a complex mechanism with several reactions taking place simultaneously. Thus, a theoretical modeling of the reaction mechanism and kinetics in the gas- and aqueous phase was performed by using the unrestricted density functional theory with the BB1K functional (employing the polarizable continuum model for the aqueous phase), unrestricted coupled cluster UCCSD(T) method, and improved canonical variational theory. Several hydrogen-bonded prereaction complexes and transition states were detected. In particular, the calculations pointed to a significant mechanistic role of the three-electron two-orbital (σ/σ* N∴O) hemibonded prereaction complexes in the aqueous phase. A good agreement with the experimental rate constants and kinetic isotope effects was achieved by downshifting the calculated reaction barriers by 3 kcal mol−1 and damping the NH(D) stretching frequency by a factor of 0.86.

28 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the kinetics of primary and secondary processes in the overall reaction of H 2S atoms with NF2 radicals from 298 to 550 K and derived the rate constants for the following elementary reactions.
Abstract: Atomic resonance absorption in the far vacuum ultraviolet and atomic resonance fluorescence have been used to investigate the kinetics of primary and secondary processes in the overall reaction of H 2S atoms with NF2 radicals from 298 to 550 K. Rate constants for the following elementary reactions have been determined directly [k298/cm3 molecule–1 s–1(1 σ)]: H + NF2 [graphic omitted] HF + NF; k1=(1.5 ± 0.2)× 10–11; O + NF2 [graphic omitted] NF + FO; k5=(1.8 ± 0.9)× 10–12; N + NF2 [graphic omitted] NF + NF; k8=(3.0 ± 1.2)× 10–12.The overall H + NF2 reactive system, containing H2, is characterised as a self-propagating chain reaction, in which the chain carriers are H, NF and F. Ground-state N 4S atoms are formed by the reaction H + NF, although these atoms play only a minor role in propagating the overall H + NF2 chain reaction. Computer modelling of the H and N atom profiles was used to obtain values for k4 and k2: H + NF [graphic omitted] HF + N; k4=(2.5 ± 0.5)× 10–13; NF + NF [graphic omitted] N2+ 2F; k2=(7.0 ± 3.5)× 10–11. Thus, the predominant decay channel for NF radicals is through rapid bimolecular disproportionation to give N2+ 2F.

28 citations

Journal ArticleDOI
TL;DR: The rate constant k1 for the reaction Cl 2P+O3→ ClO + O2(1) has been measured over the temperature range 221 −629 K as discussed by the authors.
Abstract: The rate constant k1 for the reaction Cl 2P+ O3→ ClO + O2(1) has been measured over the temperature range 221–629 K. Atomic resonance absorption with a metastable Ar lamp, which emits non-reversed thermal Cl atom lines, was used to follow the pseudo first order decay of [Cl] in excess of O3. The Arrhenius expression is given as log10(k1/cm3 molecule–1 s–1)=–(10.286 ± 0.039)–[(181 ± 12)/T]. Comparisons with other recent measurements are made.

28 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202321
202229
202185
202088
201971
201871