Theoretical Study on the Potential Energy Surface of the CH4– CO complex

Internet Electron. J. Mol. Des.2004 Abstract Motivation. Methane and carbon monoxide play important roles in atmospheric and combustion chemistry. In the atmosphere weakly bound complex will be a candidate for the green house effect due to the ability to accumulate the additional vibration energy. It is important to elucidate the intermolecular interaction between CH4 and CO. Method. The MP2 calculation are carried out for the geometry optimization and following frequency analysis of CH4 complexes with CO. Single point energies were calculated at the CCSD(T)/6-311++G(2d,2p) and MP2/augcc-pVXZ (X = D, T, and Q) levels to evaluate the basis set and electron correlation effects. Results. Interaction energies were calculated as a function of the intermolecular distance between CH4 and CO where the CO molecule approaches CH4 in the face, edge, or vertex direction. The HF potentials are calculated to be repulsive while after including the electron correlation the potentials become bound indicative of the importance of the dispersion energy for the attraction. The largest interaction energy was predicted for the face direction with oxygen-end approach of the CO molecule. On the basis of the equilibrium geometries, the structures were further optimized. Four weakly bound complexes have been found on the potential energy surface. Conclusions. The potential energy surface of the CH4-CO complex has been investigated. The Cs complex is calculated to be the most stable compared with the C3v complexes at the MP2/6-311++G(2d,2p) level. The structure of the Cs complex is in good agreement with that obtained by the microwave spectroscopy.