Article

# Potential energy surface, kinetics, and dynamics study of the Cl+CH4 -> HCl+CH3 reaction

Departamento de Química Física, Universidad de Extremadura, 06071 Badajoz, Spain.

The Journal of Chemical Physics (Impact Factor: 2.95). 04/2006; 124(12):124306. DOI: 10.1063/1.2179067 Source: PubMed

Get notified about updates to this publication Follow publication |

Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

- [Show abstract] [Hide abstract]

**ABSTRACT:**Using a recent ab initio based potential energy surface, PES-2009, quasi-classical trajectory calculations were performed to analyse the effects of the C–H stretch excitation on the reactivity and dynamics of the H + CHD3 abstraction reaction at a collision energy of 1.53 eV. Firstly, we found that the C–H stretch mode excitation has little influence on the product rotational distributions and on the scattering distribution for both channels. However, it has significant influence on the product energy distribution for the CHD2 + HD channel, indicating that the reaction shows mode selectivity, reproducing the experimental evidence. Finally, excitation of the C–H stretch by one quantum increases the reactivity of the vibrational ground-state for both channels reproducing the experimental evidence, although for the H-abstraction channel we report an enhancement of reactivity somewhat lower than other theoretical results. - [Show abstract] [Hide abstract]

**ABSTRACT:**An ab initio interpolated potential energy surface (PES) for the Cl+CH(4) reactive system has been constructed using the interpolation method of Collins and co-workers [J. Chem. Phys. 102, 5647 (1995); 108, 8302 (1998); 111, 816 (1999); Theor. Chem. Acc. 108, 313 (2002)]. The ab initio calculations have been performed using quadratic configuration interaction with single and double excitation theory to build the PES. A simple scaling all correlation technique has been used to obtain a PES which yields a barrier height and reaction energy in good agreement with high level ab initio calculations and experimental measurements. Using these interpolated PESs, a detailed quasiclassical trajectory study of integral and differential cross sections, product rovibrational populations, and internal energy distributions has been carried out for the Cl+CH(4) and Cl+CD(4) reactions, and the theoretical results have been compared with the available experimental data. It has been shown that the calculated total reaction cross sections versus collision energy for the Cl+CH(4) and Cl+CD(4) reactions is very sensitive to the barrier height. Besides, due to the zero-point energy (ZPE) leakage of the CH(4) molecule to the reaction coordinate in the quasiclassical trajectory (QCT) calculations, the reaction threshold falls below the barrier height of the PES. The ZPE leakage leads to CH(3) and HCl coproducts with internal energy below its corresponding ZPEs. We have shown that a Gaussian binning (GB) analysis of the trajectories yields excitation functions in somehow better agreement with the experimental determinations. The HCl(v'=0) and DCl(v'=0) rotational distributions are as well very sensitive to the ZPE problem. The GB correction narrows and shifts the rotational distributions to lower values of the rotational quantum numbers. However, the present QCT rotational distributions are still hotter than the experimental distributions. In both reactions the angular distributions shift from backward peaked to sideways peaked as collision energy increases, as seen in the experiments and other theoretical calculations. - [Show abstract] [Hide abstract]

**ABSTRACT:**Using an analytical potential energy surface previously developed by our group, namely PES-2002, we analyzed the gas-phase reaction between a hydrogen atom and perdeuterated methane. We studied the effect of quasiclassical trajectory (QCT) and reduced dimensionality quantum-scattering (QM) calculations, with their respective limitations, on CD3 product angular distributions in the collision energy range 16.1-46.1 kcal x mol(-1). It was found that at low collision energy, 16.1 kcal x mol(-1), both the QCT and QM calculations yielded forward scattered CD3 products, i.e., a rebound mechanism. However, at high energies only the QM calculations on the PES-2002 surface reproduced the angular scattering found experimentally.