10. Covalent Bonding and Its Effect on Magnetic Ions in Crystals 243 1. The Relevance of Covalent Bonding . . . . . . . . . . . . . 243 2. The Formation of Molecular Orbitals . . . . . . . . . . . . 244 3. Example of Molecular Orbitals Formation . . . . . . . . . 246 4. The Use of Projection Operators in the Construction ofMolecularOrbitals . . . . . . . . . . . . . . . . . . . . . 258 5. The Formation of Hybrids . . . . . . . . . . . . . . . . . . 262 6. Hybrids of the Central Ion in a Tetrahedral Complex AB4 . . . . . . . . . . . . . . . . . . . . . . . . . 267 7. Hybrids of the Central Ion in an Octahedral Complex AB6 . . . . . . . . . . . . . . . . . . . . . . . . . 269 8. The Combinations of Ligand Orbitals in an ABn Complex . . . . . . . . . . . . . . . . . . . . . . . . . 271 9. The Energy Levels of an ABn Complex . . . . . . . . . . . 274 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
11. The Quantum Theory of the Radiation Field 283 1. The Classical Electromagnetic Field . . . . . . . . . . . . . 283 2. The Quantum Theory of the Electromagnetic Field . . . . 286
12. Molecular Vibrations 295 1. The Classical Theory of Molecular Vibrations . . . . . . . 295 2. The Symmetry of the Molecules and the Normal Coordinates . . . . . . . . . . . . . . . . . . . . . 299 3. How to Find the Normal Modes of Vibration . . . . . . . . 300 4. The Use of Symmetry Coordinates . . . . . . . . . . . . . 303 5. The Quantum Theory of Molecular Vibrations . . . . . . . 307 6. The Selection Rules for Infrared and Raman Transitions, The Fermi Resonance . . . . . . . . . . . . . . . . . . . . . 309 7. The Normal Modes and the Symmetry Coordinates of a Tetrahedral Complex AB4 . . . . . . . . . . . . . . . 312 8. The Normal Modes and the Symmetry Coordinates of an Octahedral Complex AB6 . . . . . . . . . . . . . . . 315 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
13. Lattice Vibrations 323 1. The Geometry of Crystalline Solids . . . . . . . . . . . . . 323 2. Lattice Vibrations of an Infinite Crystal with One AtomPer Unit Cell . . . . . . . . . . . . . . . . . . . 326 3. Lattice Vibrations of a Finite Crystal with One AtomPer Unit Cell . . . . . . . . . . . . . . . . . . . 329 4. Lattice Vibrations of a Crystal with More Than One AtomPer Unit Cell . . . . . . . . . . . . . . . . . . . 336 5. Thermodynamics of Phonons . . . . . . . . . . . . . . . . 339 6. Phonons and Photons. Similarities and Differences . . . . 346 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
14. The Ion-Photon Interaction: Absorption and Emission of Radiation 349 1. The Ion-Radiation Interaction . . . . . . . . . . . . . . . . 349 2. The Expansion of the Interaction Hamiltonian: Different Types of Radiation . . . . . . . . . . . . . . . . . 351 3. The Density of Final States . . . . . . . . . . . . . . . . . 353 4. The Transition Probability Per Unit Time . . . . . . . . . 354 5. Dipole Radiation . . . . . . . . . . . . . . . . . . . . . . . 356 6. Selection Rules for Radiative Transitions . . . . . . . . . . 358 7. About the Intensities of Radiative Transitions . . . . . . . 369 8. The Static Effects of the Interaction Between an Atomic System and the Electromagnetic Field . . . . . 373 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 374