Elementary reaction

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

Kinetics, Energetics and OH Product Yield of the Reaction CH3O + O(3P) → CH3O*2 → Products

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.

Theoretical Study of the Reaction Mechanism and Role of Water Clusters in the Gas-Phase Hydrolysis of SiCl4

Abstract: The energies and thermodynamic parameters of the elementary reactions involved in the gas-phase hydrolysis of silicon tetrachloride were studied using ab initio quantum chemical methods (up to MP4//MP2/6-311G(2d,2p)), density functional (B3LYP/6-311++G(2d,2p)), and G2(MP2) theories. The proposed mechanism of hydrolysis consists of the formation of SiCl 4-x(OH)x (x ) 1-4), disiloxanes Cl4-x(OH)x-1Si-O-SiCl4-x(OH)x-1, chainlike and cyclic siloxane polymers [-SiCl2sO-]n, dichlorosilanone Cl2SidO, and silicic acid (HO)2SidO. Thermodynamic parameters were estimated, and the transition states were located for all of the elementary reactions. It was demonstrated that the experimentally observed kinetic features for the hightemperature hydrolysis are well described by a regular bimolecular reaction occurring through a four-membered cyclic transition state. In contrast, the low-temperature hydrolysis reaction cannot be described by the traditionally accepted bimolecular pathway for SisCl bond hydrolysis because of high activation barrier (Ea ) 107.0 kJ/mol, ¢G q ) 142.5 kJ/mol) nor by reactions occurring through three- or four-molecular transition states proposed earlier for reactions occurring in aqueous solution. The transition states of SiCl 4 with oneand two-coordinated water molecules were located; these significantly decrease the free energy of activation ¢G q (to 121.3 and 111.5 kJ/mol, correspondingly). However, this decrease in ¢G q is not sufficient to account for the high value of the hydrolysis rate observed experimentally under low-temperature conditions.

Elementary kinetics of nitrogen electroreduction on Fe surfaces

Abstract: Electrochemical ammonia synthesis could provide a sustainable and efficient alternative to the energy intensive Haber-Bosch process. Development of an active and selective N2 electroreduction catalyst requires mechanism determination to aid in connecting the catalyst composition and structure to performance. Density functional theory (DFT) calculations are used to examine the elementary step energetics of associative N2 reduction mechanisms on two low index Fe surfaces. Interfacial water molecules in the Heyrovsky-like mechanism help lower some of the elementary activation barriers. Electrode potential dependent barriers show that cathodic potentials below -1.5 V-RHE (reversible hydrogen electrode) are necessary to give a significant rate of N2 electroreduction. DFT barriers suggest a larger overpotential than expected based on elementary reaction free energies. Linear Bronsted-Evans-Polanyi relationships do not hold across N-H formation steps on these surfaces, further confirming that explicit barriers should be considered in DFT studies of the nitrogen reduction reaction.

Kinetic studies for diatomic free radicals using mass spectrometry. Part 3.—Elementary reactions involving BrO X2Π radicals

Abstract: Elementary reactions involving BrO X2Π radicals have been studied at 298 K in a discharge-flow system linked to a mass spectrometer with collision-free sampling. Detection of BrO was made directly by means of the BrO+ ion current, calibrated in terms of absolute BrO concentrations using the rapid reaction (1), NO + BrO [graphic omitted] NO2+Br.(1) Rate constants at 298 K (cm3 molecule–1 s–1) are reported for the second order decay reaction (2), BrO + BrO [graphic omitted] 2 Br + O2(2) as well as for reaction (1): k1=(2.2 ± 0.4)× 10–11; k2=(6.4 ± 1.3)× 10–12 cm3 molecule s–1. In addition, the rate constant k3 for reaction of Br 2P3/2 atoms with O3(3), has been determined at 298 K: Br + O3 [graghic omitted] BrO + O2(3), k3=(1.2 ± 0.2)× 10–12 cm3 molecule–1 s–1.