Ideas of Quantum Chemistry P88 shows how quantum mechanics is applied to chemistry to give it a theoretical foundation. The structure of the book (a TREE-form) emphasizes the logical relationships between various topics, facts and methods. It shows the reader which parts of the text are needed for understanding specific aspects of the subject matter. Interspersed throughout the text are short biographies of key scientists and their contributions to the development of the field. | 836 14. Intermolecular Motion of Electrons and Nuclei Chemical Reactions despite the multidimensionality of the problem eq. is still valid . VR - VP is a single variable describing the position of system on the electrontransfer reaction path it is therefore a collective coordinate that describes the positions of the solvent molecules . mean force potential No doubt the potential energy value is important but how often can this value be reached by the system is equally important. This is connected to the width of the low-energy basin associated with the entropy36 and to the free energy. In statistical thermodynamics we introduce the idea of the potential of the mean force related to the free energy. Imagine a system in which we have two motions on different time scales fast . of small solvent molecules and slow . which change the shape of a macromolecule . To focus on the slow motion we average the energy over the fast motions the Boltzmann factor will be needed which will introduce a temperature dependence on the resulting energy . In this way from the potential energy we obtain the mean force potential depending only on the slow variables sometimes called the free energy which is a function of geometry of the macromolecule cf. p. 293. The second Marcus assumption is that the ordinate axis should be treated as the mean force potential or the free energy rather than just potential energy. It is very rare in theoretical chemistry86 87 that a many-dimensional problem can be transformed to a single variable problem. This is why the Marcus idea described above of a collective coordinate provokes the reaction no way . However as it turned out later this simple postulate lead to a solution that grasps the essential features of electron transfer. What do the Marcus parabolas mean The example just considered of the electron transfer reaction Fe2 Fe3 Fe3 Fe2 reveals that in this case the reaction barrier is controlled by the solvent . by billions of .
