equilibrium before undergoing significant reaction progress. However, for most thermal reactions, it is remarkably successful In this theory, one views the reactants as undergoing collisions that act to keep all of their degrees of freedom(translational, rotational, vibrational, electronic)in thermal equilibrium. Among the collection of such reactant molecules, at any instant of time some will have enough internal energy to access a transition state (ts)on the born Oppenheimer ground state potential energy surface. Within tsT, the rate of progress from reactants to products is then expressed in terms of the concentration of species that exist near the Ts multiplied by the rate at which these species move through the ts region of the energy surface The concentration of species at the Ts is, in turn, written in terms of the equilibrium constant expression of statistical mechanics discussed in Chapter 7. For example, for a bimolecular reaction A+B>C passing through a ts denoted ab one writes the concentration(in molecules per unit volume)of AB species in terms of the concentrations of A and of b and the respective partition functions as AB=(qAB/V(V(BVAjB2 equilibrium before undergoing significant reaction progress. However, for most thermal reactions, it is remarkably successful. In this theory, one views the reactants as undergoing collisions that act to keep all of their degrees of freedom (translational, rotational, vibrational, electronic) in thermal equilibrium. Among the collection of such reactant molecules, at any instant of time, some will have enough internal energy to access a transition state (TS) on the Born￾Oppenheimer ground state potential energy surface. Within TST, the rate of progress from reactants to products is then expressed in terms of the concentration of species that exist near the TS multiplied by the rate at which these species move through the TS region of the energy surface. The concentration of species at the TS is, in turn, written in terms of the equilibrium constant expression of statistical mechanics discussed in Chapter 7. For example, for a bimolecular reaction A + B ® C passing through a TS denoted AB*, one writes the concentration (in molecules per unit volume) of AB* species in terms of the concentrations of A and of B and the respective partition functions as [AB*] = (qAB*/V)/{(qA/V)( qB /V)} [A] [B]