Transition state theory can be employed by extracting the free energy barrier along the reaction coordinate, from the potential of mean force (PMF), F (R) that is defined as 322 e -βF (R) ≡ dP dp c dp k dq c dx k e -βHPF , (195) using the classical limit of the Hamiltonian H PF (Eq. 192). Note that all phase space variables are integrated except the reaction coordinate R. The barrier along the PMF, ∆F ‡ = F (R ‡ ) -F (R 0 ), is computed from its value at the reactant well, R 0 , and the barrier, R ‡ . The chemical rate using ∆F ‡ within transition state theory is then written as, 322,374