Computational studies on the kinetics and mechanisms for NH3 reactions with ClOx (x=0-4) radicals
ABSTRACT Kinetics and mechanisms for NH3 reactions with ClOx (x = 0-4) radicals have been investigated at the G2M level of theory in conjunction with statistical theory calculations. The geometric parameters of the species and stationary points involved in the reactions have been optimized at the B3LYP/6-311+G(3df,2p) level of theory. Their energetics have been further refined with the G2M method. The results show that the H-abstraction process is the most favorable channel in each reaction and the barriers predicted in decreasing order are OClO > ClO > Cl > ClO3 > ClO4. All reactions were found to occur by hydrogen-bonding complexes; the rate constants for these complex metathetical processes have been calculated in the temperature range 200-2000 K by the microcanonical VTST and/or RRKM theory (for ClO4 + NH3) with Eckart tunneling and multiple reflection corrections. The predicted rate constants are in good agreement with the available experimental data.
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ABSTRACT: A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 (2011)] or molecules [Chin. Phys. Lett. 29 080504 (2012)] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.Chinese Physics B 04/2014; 23(5):050501. DOI:10.1088/1674-1056/23/5/050501 · 1.39 Impact Factor
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ABSTRACT: The kinetics and mechanisms for N2H4 + NOx, (x = 1-3) reactions and the related reverse reactions have been investigated by ab initio molecular orbital theory based on the CCSD(T)/CBS/ICCSD/6-31G(d,p), CCSD(T)//B3LYP and CCSD(T)//BH&HLYP methods with the 6-311++G(3df,2p) basis set. These reactions are important to the propulsion chemistry of the N2H4-N2O4 propellant system. The results show that the reactions of N2H4 with NO and NO2 producing N2H3 + HNO and N2H3 + c-HONO by H-abstraction with 33.7 and 10.3 kcal/mol barriers, respectively, are dominant. For the N2H4 + NO3(D-3h) reaction via two pre-reaction van der Waals complexes with 0.5 kcal/mol and -1.6 kcal/mol binding energies produces HNO3 + N2H3 by H-abstraction and t-HONO + N2H3O by concerted O- and H-atom transfers, respectively. The predicted enthalpies of formation of various products at 0 K are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and some key reverse reactions have been predicted in the temperature range 300-2000 K with tunneling corrections using transition state theory (for direct abstraction) and variational Rice-Ramsperger-Kassel-Marcus theory (for association! decomposition) by solving the master equation.Computational and Theoretical Chemistry 10/2014; 1046:73–80. DOI:10.1016/j.comptc.2014.07.011 · 1.37 Impact Factor
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ABSTRACT: Six reaction systems relevant to the atmosphere and the ammonium perchlorate combustion chemistry have been studied. The systems include the bimolecular reactions of ClO with HO, HO2, ClO, OClO, NO and NO2 and some of their reverse processes. The geometries of the reactants, intermediates, transition states and products involved in these reactions were optimized at the B3LYP/6-311+G(3df, 2p) level and final energies were refined at the modified Gaussian – 2 (G2M) or CCSD(T)/6-311+G(3df, 2p) level.Temperature/pressure-dependent rate constants for major product channels have been predicted and compared with the available experimental data. Detailed mechanisms for these reactions have been discussed on the basis of predicted potential energy surfaces. The calculated geometrical parameters, heats of formation and rate constants are quite satisfactory and in good agreement with available experimental data. For practical applications, the heats of formation of the key species, and the rate constants for all the major reactions discussed under different conditions have been recommended.ChemInform 05/2011; 965(s 2–3):328–339. DOI:10.1016/j.comptc.2010.12.002