Figure captions Figure 1. The energy of a reaction along the reaction path. The zero point energy is included. The reactants are on the left and the products are on the right and are separated by an energy barrier of height Δ E $^{‡}$. At the pass over which the reactants must pass for the reaction to proceed, the reacting molecules form a transient complex that Eyring called an activated complex. Figure 2. Heat capacity of argon, as obtained from Eq. (6), compared with experiment. 11