Charge Transfer Processes in Condensed Media

Molecules in liquid and solid media are exposed to strong inter­ action forces from the surrounding medium. The formulation of a comprehensive theory of chemical processes in condensed media is consequently an elaborate task involving concepts from several areas of the natural sciences. Within the las~ two and a half decades very notable results towards the formulation of a 'unified' quantum mechanical theory of such processes have in fact been achieved, and by the variety of physical, chemical, and biological processes which can be suitably covered by this framework, the new theory represents an adequate alternative to the transition state theory. The present work has a two-fold purpose. Firstly, to provide a reasonably organized exposition of some basic aspects of these developments. This part emphasizes the fundamental similarities between chemical and other kinds of radiationless processes and includes the derivation of the most important rate expressions without resorting to involved mathematical techniques. The s- ond major purpose is to illustrate the 'unified' character of the rate theory by analysis of a considerable amount of expe- mental data from both 'conventional' kinetics and from such untraditional areas as low-temperature, strongly exothermic, and biological processes. Particular attention is here given to those systems for which a classical description is inadequate, and which provide a diagnostic distinction between several alternative theoretical approaches.

1 Introduction.- 1.1 Nature of Elementary Chemical Processes.- 1.2 Development of Theories for Elementary Chemical Processes.- 1.3 Chemical Reactions as a Class of Radiationless Processes.- 2 Multiphonon Representation of Continuous Media.- 2.1 Nature of Solvent Configuration Fluctuations.- 2.2 Interaction with Ionic Charges.- 2.3 Relation to Macroscopic Parameters.- 3 Quantum Mechanical Formulation of Rate Theory.- 3.1 Elements of Scattering Theory.- 3.2 Channel States and Nature of the Perturbation.- 3.3 Evaluation of Transition Matrix Elements.- 3.3.1 Harmonic Oscillator Representation.- 3.4 The Role of a Continuous Vibration Spectrum.- 3.5 Relation to Experimental Data.- 3.5.1 The Electronic Factor.- 3.5.2 Intramolecular and Medium-induced Electronic Relaxation.- 3.6 Lineshape of Optical Transitions.- 4 The Effect of Intramolecular Modes.- 4.1 Special Features of Electron Transfer Processes.- 4.2 Quantum Modes in Electron Transfer Reactions.- 4.2.1 Displaced Potential Surfaces..- 4.2.2 Effects of Frequency Changes.- 4.2.3 Effects of Anharmonicity.- 4.3 Relation to Experimental Data.- 5 Semiclassical Approximations.- 5.1 One-Dimensional Nuclear Motion.- 5.1.1 Classical Nuclear Motion.- 5.1.2 Nuclear Quantum Effects.- 5.2 Many-Dimensional Nuclear Motion.- 5.3 Relation to Experimental Data.- 5.3.1 Outer Sphere Electron Transfer Processes.- 5.3.2 Nucleophilic Substitution Reactions.- 6 Atom Group Transfer Processes.- 6.1 General Features of Nuclear Motion.- 6.2 Semiclassical Approaches to Atom Group Transfer.- 6.3 Quantum Mechanical Formulation of Atom Group Transfer.- 6.3.1 Nuclear Tunnelling between Bound States.- 6.3.2 Adiabatic and Nonadiabatic AT.- 6.3.3 Relation to the Gamov Tunnelling Factor.- 6.4 Relation to Experimental Data.- 7 Higher Order Processes.- 7.1 Higher Order Processes in Chemical ET Reactions.- 7.2 Theoretical Formulation of Higher Order Rate Probability.- 7.2.1 Semiclassical Methods..- 7.2.2 The Effect of High-Frequency Modes..- 7.2.3 Adiabatic Second Order Processes.- 7.2.4 Quantum Mechanical Formulation.- 7.3 Relation to Experimental Data.- 8 Electrochemical Processes.- 8.1 Fundamental Properties of Electrochemical Reactions.- 8.1.1 The nonuniform dielectric medium.- 8.1.2 The continuous electronic spectrum.- 8.1.3 Adiabaticity effects in many-potential surface systems.- 8.2 Quantum Mechanical Formulation of Electrode Kinetics.- 8.2.1 Metal electrodes.- 8.2.2 Semiconductor electrode.- 8.3 Relation to Experimental Data.- 8.3.1 The current-voltage relationship.- 8.3.2 The nature of the substrate electrode.- 8.3.3 The electrochemical hydrogen evolution reaction (her).- 8.4 Electrode Processes at Film Covered Electrodes.- 8.4.1 Tunnelling mechanisms.- 8.4.2 Mobility mechanisms.- 9 Application of the Rate Theory to Biological Systems.- 9.1 General.- 9.2 Specific Biological Electron Transfer Systems.- 9.2.1 Primary Photosynthetic Events.- 9.2.2 Bioinorganic ET Reactions.- 9.3 Electronic Conduction in Biological Systems.- 9.4 Conformational Dynamics.- A1.- A1.1 Derivation of the Sum Rules(eq.(2.49)).- A1.2 Derivation of Eq.(2.56).- References.