In addition to the stationary points, the reaction path from reactants to products was also calculated. However, due to the very high computational cost of the CCSD(T)-F12a/aug-cc-pVTZ level and our computational limitations, we explored more economic alternatives, second order Møller-Plesset perturbation theory, MP2/6-31G(d,p). At this low level, we began by locating and characterizing all the stationary points. Next, starting from the saddle point, the reaction valley was constructed using 50 points, calculating energy, gradient and Hessian matrices at each point between s=-3.0 bohr (in the reactant side) and s=+3.0 bohr (in the product side), where the reaction coordinate, s, is defined as the signed distance from the saddle point, s = 0. So, we describe the reaction path and orthogonal motions at these 50 points. In numerical terms, the Hessian matrix represents a 30x30 matrix, corresponding to 10 atoms times 3 Cartesian coordinates, in total 900 energies per point, and since 50 points were calculated, this effort is equivalent to about 45 000 energy calculations. Note, however, that at the MP2 level fortunately the second energy derivatives are analytical, which is equivalent to a noticeably lower computational effort. As a simple test of quality of this method, we compared some properties of the stationary points with the most accurate CCSD(T)-F12/aug-cc-pVTZ single-point calculations. The MP2 method gives a reaction energy of -40.45 kcal mol -1 as compared to -23.12 kcal mol -1 at the highest level, and a barrier height of +0.31 kcal mol -1 as compared to +0.21 kcal mol -1 . Clearly, the energetic description must be improved.