reaction. The weight of state 4 is significant near the transition state and negligible in both reactant and product sides. It also shows that state 5 has a relatively small contribution along the IRC. Thus, it is sufficiently accurate to consider only the first five lowest lying electronic states for F / Cl + H2O reactions. Another useful and efficient test is to plot some one-dimensional potentials in the entrance or exit channels. For instance, the potential energy changes along the center of mass distance between reactants or between products at different orientations. As shown in Figure , for F and H2O