Transition state structure, barrier height, and vibrational frequencies for the reaction Cl+CH4→CH3+HCl

We have carried out ab initio calculations using second- and fourth-order Mo/ller–Plesset perturbation theory, scaled electron correlation, and several basis sets for the reaction Cl+CH4→CH3+HCl. We found that including electron correlation is essential for obtaining accurate barrier heights and vibrational frequencies. Furthermore, scaling the correlation energy further improves the barrier height predictions provided that the basis set being used is correlation balanced for both bonds involved in the reaction. Geometries and transition state frequencies calculated at the MP2 and MP-SAC2 levels with the most extensive and best balanced basis set are in good agreement with one another for all bound modes, but the unbound-mode frequency changes by 214i cm−1.