Ab initio calculations: a significant route to identify the transition states, entrance and exit channel complexes, and activation energies

Ab initio calculations have been used to identify the potential energy minimum of the entrance and exit channel complexes and transition state structure in the hydrogen abstraction reaction of CH4 with OH radical, as well as activation energy and reaction enthalpy were computed. MP2/6- 31G** and HF/6-31G** levels have been used to optimized geometries and harmonic vibrational frequencies. The product complex is at a lower energy level than reactant complex (- 304193.2414 KJMOL vs -304144.0172 KJ/MOL) at MP2 level, so the exit channel complex is more stable than entrance complex. The activation barrier is 45.9161 KJ/MOL and the enthalpy change is -49.2242 KJ/MOL at MP2 level