The hydrogen abstraction reaction H+CH4. II. Theoretical investigation of the kinetics and dynamics

Departamento de Química Física, Universidad de Extremadura, Badajoz, Spain.
The Journal of Chemical Physics (Impact Factor: 2.95). 06/2009; 130(18):184315. DOI: 10.1063/1.3132594
Source: PubMed


On a new potential energy surface (PES-2008) developed by our group (preceding paper), we performed an extensive kinetics study using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range of 250-2000 K and a dynamics study using quasiclassical trajectory (QCT) and quantum-mechanical (QM) calculations at collision energies between 0.7 and 2.0 eV for the title reaction and isotopically substituted versions. Kinetically, the H + CH(4) forward and reverse thermal rate constants reproduce the available experimental data, with a small curvature of the Arrhenius plot indicating the role of tunneling in this hydrogen abstraction reaction. Five sets of kinetic isotope effects are also calculated. In general, they reproduce the experimental information. Dynamically, we focused on the H + CD(4) reaction because there are more experimental studies for comparison. Most of the available energy appears as product translational energy (55%-68%), with the HD product being vibrationally cold (v(')=0,1) in agreement with experiment, although rotationally hotter than experiment. The reaction cross section is practically negligible at 0.7 eV and still small at 1.5 eV, reproducing the experimental evidence, although our values are smaller. The product angular distribution is analyzed using QCT and QM methods. While at low energies (0.7 eV) both the QCT and the QM calculations yield forward scattered CD(3) product, i.e., a rebound mechanism, at high energy (1.2 eV) only the QM calculations reproduce the experiment. The agreement with this wide variety of kinetic and dynamic experimental data (always qualitative and in some cases quantitative) shows the capacity of the PES-2008 surface to describe the reaction system.

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Available from: Jose C Corchado, May 23, 2014
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    • "-of-plane bending and valence bending terms and it was constructed by a multi-beginning least-squares optimisation of the parameters to CCSD(T)/cc-pVTZ energies and derivatives. The PES-2009 was subjected to great variety of tests [8] [9] [10], with both kinetics and dynamics (QCT and QM) results compared with the experimental information available for the H + CH 4 reaction and its isotopomers. In general, PES-2009 reproduced the wide variety of experimental properties, which lent confidence to the surface. "
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