Elementary reaction

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

Weak Collision Effects in the Reaction CH3CO → CH3 + CO

Abstract: Rate constants for the unimolecular decomposition of CH3CO have been obtained as a function of temperature (420 - 500 K) and helium density (3 - 18 · 1016 atom cm−3), conditions which are in the second order region of the fall-off curve. An Arrhenius expression for the low-pressure limit unimolecular rate constant was obtained from the results, k1±(He) = (6.7 ± 1.8) · 10−9 exp[(-6921 ± 126 K)/T] cm3 molecule−1 s−1. Using a Master Equation formalism to calculate values of k1, a set of the two energy parameters needed in the calculations, E± and ΔE)down (including its temperature dependence), was found that is within the range of expected values (including a temperature dependence in the case of ΔEdown), which, when incorporated into the Master Equation, provides calculated rate constants which agree well with the measured ones. They are E± = 65.3 ± 4.0 kJ mol−1 and ΔEdown = 65.6 + 0.271 T cm−1 (the latter, a parameterized expression, is valid only in the temperature range of this study). A transition state model for the unimolecular decomposition of CH3CO was produced which provides high-pressure limit rate constants for this reaction (k1±(CH3CO ± CH3 + CO) = 2.50 · 1013 exp(-8244 K/T) s−1 and k−1±(CH3 + CO ± CH3CO) = 7.64 · 10−13 exp(-3073 K/T) cm3 molecule−1 s−1) and k(E) values for solving the Master Equation for reaction conditions that are in the fall-off region. Fall-off behavior of k1 and k−1 reported by others for several different bath gases was reproduced within the uncertainty limits of the experimental results using the Master Equation formalism incorporating the transition state model, the energy parameter E± given above, and reasonable values for ΔEdown for the different bath gases used. This Master Equation formalism and transition state model should provide unimolecular rate constants for reaction (1, - 1) in the fall-off region for additional bath gases using reasonable estimates of ΔEdown (e. g., values obtained for this energy-transfer parameter for collisions between other polyatomic radicals and the bath gases of interest).

Shock-tube study of the reaction of rich mixtures of benzene and oxygen

Abstract: The kinetic effects of a small amount of oxygen on the pyrolysis of benzene were studied,using shock tubes to obtain information on the elementary reactions essential to the combustion kinetics of benzene. Both single-pulse type shock-tube and optical experiments were carried out. The temperature range was 1300°–1700°K, the ratio of oxygen to benze was 0–1, the concentration of benzene was 10 −3 –10 −4 mol/l, and the reaction time was 200 μ sec−1 msec. Provided that the concentration of oxygen is sufficiently low, the rate law can be expressed as− d (C 6 H 6 )/ dt = k I (C 6 H 6 ) 2 + k II (C 6 H 6 )(O 2 ) and − d (O 2 )/ dt = k III (C 6 H 6 )(O 2 ). The apparent rate constants are found to be k I =10 9.5 exp(−30±5 kcal/ RT ) l mol −1 sec −1 , k II =10 11.0 exp(−35±5 kcal/ RT ) l mol −1 sec −1 , k III =10 9.0 exp(−23±5 kcal/ RT ) l mol −1 sec −1 . Under these experimental conditions, little water was formed. Carbon monoxide andacetylene were formed by reaction of the phenyl radical and oxygen; biphenyl and higher polymers were formed almost the same way as in pyrolysis. A kinetic scheme which accounts for the above experimental facts is proposed.

An Experimental Study of the Reactions CH3CHO + Cl, C2H4O + Cl, and C2H4O + F in the Gas-Phase

Abstract: The reactions of chlorine and fluorine atoms with the structural isomers CH3CHO and C2H4O have been studied at low pressures and room temperature by the discharge flow technique with mass spectrometric detection. Using the reference reactions the relative rate constant for the reactions were determined: k1/k0 = 1.04 ± 0.09, k2/k0 = 0.49 ± 0.04, k3/k00 = 0.47 ± 0.05. — Reaction (1) proceeds mainly via hydrogen abstraction from the aldehyde group (> 93%) forming CH3CO. In the reactions of ethylene oxide (2), (3) the abstraction route is observed, contributions from addition channels in reaction (2) are discussed.

Determination of Rate Constants and Product Branching Ratios for the Reactions of CH3O2 and CH3O with Cl Atoms at Room Temperature

Abstract: Reactions of CH 3 O 2 and of CH 3 O radicals with Cl atoms have been investigated at 300 K using a discharge flow system with LIF and mass-spectrometric detection. CH 3 O 2 + Cl → OCl + CH 3 O (1a) → HCl+CH 2 O 2 (1b) CH 3 O + Cl → HCl + HCHO (2) Rate constants k 1 = (1.15 ± 0.3).10 -10 and k 2 = (1.00 ± 0.2).10 -10 , in units cm 3 molecule -1 s -1 , have been obtained observing pseudo-first-order decays of CH 3 O 2 and CH 3 O radicals, respectively. The branching ratio k 1a /k 1 = 0.51 ± 0.09 has been found from the determination of OCl yields. Formation of the Criegee intermediate CH 2 O 2 in reaction (1b) was inferred from CO 2 generation. A lower limit of 0.8±0.5 was derived for the CO 2 yield from unimolecular CH 2 O 2 decomposition. Possible reaction pathways for steps (1a) and (1b) are suggested on the basis of ab initio model calculations. The calculations include the estimation of structures and energies of intermediate CH 3 O 2 Cl collision complexes and the decomposition of CH 3 OOCl to yield products.

New approaches to the deduction of complex reaction mechanisms.

Abstract: The formulation of a macroscopic reaction mechanism, the sequence of elementary reaction steps by which reactants are turned into products, is difficult. We review several new methods of determining the causal connectivity of chemical species, the reaction pathway (the sequence of chemical species), and the reaction mechanisms of complex reaction systems from prescribed measurements and theories.