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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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TL;DR: The reactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling of MMH homogeneous decomposition at atmospheric conditions and an elementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literature data was developed.
Abstract: The reaction kinetics for the thermal decomposition of monomethylhydrazine (MMH) was studied with quantum Rice-Ramsperger-Kassel (QRRK) theory and a master equation analysis for pressure falloff. Thermochemical properties were determined by ab initio and density functional calculations. The entropies, S degrees (298.15 K), and heat capacities, Cp degrees (T) (0 < or = T/K < or = 1500), from vibrational, translational, and external rotational contributions were calculated using statistical mechanics based on the vibrational frequencies and structures obtained from the density functional study. Potential barriers for internal rotations were calculated at the B3LYP/6-311G(d,p) level, and hindered rotational contributions to S degrees (298.15 K) and Cp degrees (T) were calculated by solving the Schrodinger equation with free rotor wave functions, and the partition coefficients were treated by direct integration over energy levels of the internal rotation potentials. Enthalpies of formation, DeltafH degrees (298.15 K), for the parent MMH (CH3NHNH2) and its corresponding radicals CH3N*NH2, CH3NHN*H, and C*H2NHNH2 were determined to be 21.6, 48.5, 51.1, and 62.8 kcal mol(-1) by use of isodesmic reaction analysis and various ab initio methods. The kinetic analysis of the thermal decomposition, abstraction, and substitution reactions of MMH was performed at the CBS-QB3 level, with those of N-N and C-N bond scissions determined by high level CCSD(T)/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) calculations. Rate constants of thermally activated MMH to dissociation products were calculated as functions of pressure and temperature. An elementary reaction mechanism based on the calculated rate constants, thermochemical properties, and literature data was developed to model the experimental data on the overall MMH thermal decomposition rate. The reactions of N-N and C-N bond scission were found to be the major reaction paths for the modeling of MMH homogeneous decomposition at atmospheric conditions.
29 citations
TL;DR: The current study shows that the kinetics of β-lg denaturation can be far more complicated than that described by the simple rate equation commonly applied in previous literature.
29 citations
TL;DR: In this article, the four chlorinated methanes (methyl chloride, methylene chloride, chloroform, and carbon tetrachloride) were used as models of chlorocarbons with Cl/H ratios of 00196 to 0083 to investigate their thermal stability and hydrodechlorination in excess hydrogen.
29 citations
01 Jan 1988
TL;DR: In this paper, the one-step reaction mechanism, CO+1/2O2→CO2 with d [C O ] / d t = − k o υ [ C O ] a [ H 2 O ] b [ O 2 ] c which is frequently used in combustion problems when simplified chemistry is necessary, is numerically studied in order to define its limitations and understand the chemical and physical reasons for these limitations.
Abstract: The one-step reaction mechanism, CO+1/2O2→CO2 with d [ C O ] / d t = − k o υ [ C O ] a [ H 2 O ] b [ O 2 ] c which is frequently used in combustion problems when simplified chemistry is necessary, is numerically studied in order to (i) define its limitations (and therefore usage) and (ii) understand the chemical and physical reasons for these limitations. The analysis is carried out with the aid of a validated comprehensive, elementary reaction mechanism for moist CO oxidation and by specialized sensitivity coefficients which correlate the parameters of the global model to the parameters of the elementary model. The results confirm many of the previous, empiricially derived, literature models and show the overall rate constant, as a function of temperature, to exhibit non-Arrhenius kinetics and to be dependent on pressure and mixture equivalence ratio. More importantly, models derived from temporally reacting systems are shown to be improper for use in modeling systems reacting with transport phenomena. The specialized sensitivity coefficients are used to explain these complex behaviors in the overall model. For the temporal system, these coefficients show that the global model must be able to account for dissociation and equilibration at high temperatures, for explosion phenomena in the intermediate temperatures, and for reaction of carbon monoxide with both the hydroxyl radical and hydroperoxy radical at low temperatures. Lastly, methods for modifying the existing model or for developing a new model are suggested.
29 citations
TL;DR: In this paper, the authors analyze the reaction kinetics in the situation when the surface contains steps and show that the contribution of steps to the reaction rate may be appreciable. But they do not consider the effect of communication between terraces and steps.
29 citations