1. The Adiabatic Approximation.- 1. The Adiabatic Approximation [3, 4, 48].- 2. Molecular Energy Levels and Potential Curve Diagrams. The Harmonic Approximation.- 3. Lattice Vibration Theory for a Crystal Containing Impurities. Band and Localized Vibrations. Pseudolocalized Vibrations.- 4. Vibronic Transition Probabilities. The Franck - Condon Principle.- 2. Theory of Quasiline Vibronic Spectra of Impurity Centers.- 5. The Impurity Center Model.- 6. The Energy of a Purely Electronic Transition, Zero-Phonon Transitions, and Quasilines.- 7. The Integrated Intensity of the Purely Electronic Line and Its Temperature Dependence in the Simplest Case.- 8. Position, Width, and Peak Intensity of the Purely Electronic Line in the Simplest Case.- 9. The Integrated Intensity of a Vibronic Band.- 10. One-Phonon Transitions.- 11. Two-Phonon and Multiphonon Transitions.- 12. The Purely Electronic Line and the Vibrational Background.- 13. The Effect of Localized Vibrations.- 14. Several Localized Vibrations.- 15. Structure of the Vibrational Background. Role of Pseudolocalized Vibrations and Singularities in the Frequency Spectrum of the Band Vibrations.- 16. Characteristic Patterns of Vibrational Structure.- 17. Summary of the Results for the Basic Model. The Need for Improved Theories.- 3. The Relation between Vibronic Spectra and Mössbauer Spectra.- 18. The Mössbauer Effect.- 19. Derivation of the Basic Equations for the Vibrational Structure of the Gamma Transition Spectrum.- 20. Integrated Intensity of the Vibrational Band in a Gamma Transition.- 21. The Integrated Intensity of the Mössbauer Line and Its Temperature Dependence.- 22. General Relation between the Mössbauer Effect and Vibronic Spectra.- 23. The Role of Localized and Pseudolocalized Vibrations. Comparison withthe Shpol'skii Effect.- 4. Vibronic Spectra in Improved Versions of the Theory.- 24. Oscillator Strength of the Electronic Transition Dependent on the Vibrational Displacement in the Crystal (Deviation from the Condon Approximation).- 25. Anharmonic Vibrations.- 26. Force Constant Changes.- 27. Nonadiabatic Vibronic Interaction.- 28. Effects of the Inhomogeneous Structure of the Host Crystal.- 29. The Isotope Shift.- 30. The Shape of the Purely Electronic Line. The Nature of the Broadening [144].- 5. Infrared Absorption and Light Scattering Spectra.- 31. Infrared Absorption by Point Lattice Defects.- 32. Light Scattering by Impurity Centers.- Appendix I. The Franck - Condon Principle.- I.1 The Franck - Condon Principle in the Theory of Vibronic Transitions.- I.2 The Semiclassical Franck - Condon Principle and the Mössbauer Effect.- Appendix II. Some Concepts from the Theory of Small Vibrations.- II.1 Small Vibrations of a System of Material Points.- II.2 Eigenfrequencies, Normal Modes, and Normal Coordinates.- II.3 Repeated Roots of the Characteristic Equation.- II.4 Classical Pattern of Small Vibrations.- II.5 Normal Coordinates and the Quantum-Mechanical Problem of Small Vibrations.- II.6 The Effects of a Localized Change in the Dynamics on the Normal Modes.- II.7 Suppression of the Band Vibrations in the Presence of Localized Vibrations.- II.8 Localized Lattice Dynamics in the Neighborhood of a Defect and Pseudolocalized Vibrations.- Appendix III. Some Sum Formulas.- Appendix IV. A Table of the Limiting Vibration Frequencies for Certain Ionic Crystals.- Appendix V. The Proportionality Coefficient between the Transition Probability and the Square of the Matrix Element of the Perturbation Operator in the Quantum Theory of Radiation.- Appendix VI. The Methodof Moments.- Appendix VII. The Adiabatic Approximation and the Variational Principle.- VII.1 Derivation of the Adiabatic Approximation from the Variational Principle.- VII.2 Inequalities for the Energy Eigenvalues.- VII.3 The Hellmann - Feynman Theorem.- References.- Supplementary References.
