A thorough knowledge of the physics of atoms and quanta is clearly a must for every student of physics but also for students of neighbouring disciplines such as chemistry and electrical engineering. What these students especially need is a coherent presenta­ tion of both the experimental and the theoretical aspects of atomic and quantum physics. Indeed, this field could evolve only through the intimate interaction between ingenious experiments and an equally ingenious development of bold new ideas. It is well known that the study of the microworld of atoms caused a revolution of physical thought, and fundamental ideas of classical physics, such as those on measur­ ability, had to be abandoned. But atomic and quantum physics is not only a fascinating field with respect to the development of far-reaching new physical ideas. It is also of enormous importance as a basis for other fields. For instance, it provides chemistry with a conceptual basis through the quantum theory of chemical bonding. Modern solid-state physics, with its numerous applications in communication and computer technology, rests on the fundamental concepts first developed in atomic and quantum physics. Among the many other important technical applications we mention just the laser, a now widely used light source which produces light whose physical nature is quite different from that of conventional lamps. In this book we have tried to convey to the reader some of the fascination which atomic and quantum physics still gives a physicist studying this field.

1. Introduction.- 1.1 Classical Physics and Quantum Mechanics.- 1.2 Short Historical Review.- 2. The Mass and Size of the Atom.- 2.1 What is an Atom?.- 2.2 Determination of the Mass.- 2.3 Methods for Determining Avogadro's Number.- 2.3.1 Electrolysis.- 2.3.2 The Gas Constant and Boltzmann's Constant.- 2.3.3 X-Ray Diffraction in Crystals.- 2.3.4 Determination Using Radioactive Decay.- 2.4 Determination of the Size of the Atom.- 2.4.1 Application of the Kinetic Theory of Gases.- 2.4.2 The Interaction Cross Section.- 2.4.3 Experimental Determination of Interaction Cross Sections.- 2.4.4 Determining the Atomic Size from the Covolume.- 2.4.5 Atomic Sizes from X-Ray Diffraction Measurements on Crystals.- 2.4.6 Can Individual Atoms Be Seen?.- Problems.- 3. Isotopes.- 3.1 The Periodic System of the Elements.- 3.2 Mass Spectroscopy.- 3.2.1 Parabola Method.- 3.2.2 Improved Mass Spectrometers.- 3.2.3 Results of Mass Spectrometry.- 3.2.4 Modern Applications of the Mass Spectrometer.- 3.2.5 Isotope Separation.- Problems.- 4. The Nucleus of the Atom.- 4.1 Passage of Electrons Through Matter.- 4.2 Passage of Alpha Particles Through Matter (Rutherford Scattering).- 4.2.1 Some Properties of Alpha Particles.- 4.2.2 Scattering of Alpha Particles by a Foil.- 4.2.3 Derivation of the Rutherford Scattering Formula.- 4.2.4 Experimental Results.- 4.2.5 What is Meant by Nuclear Radius?.- Problems.- 5. The Photon.- 5.1 Wave Character of Light.- 5.2 Thermal Radiation.- 5.2.1 Spectral Distribution of Black Body Radiation.- 5.2.2 Planck's Radiation Formula.- 5.2.3 Einstein's Derivation of Planck's Formula.- 5.3 The Photoelectric Effect.- 5.4 The Compton Effect.- 5.4.1 Experiments.- 5.4.2 Derivation of the Compton Shift.- Problems.- 6. The Electron.- 6.1 Production of Free Electrons.- 6.2 Size of the Electron.- 6.3 The Charge of the Electron.- 6.4 The Specific Charge e/m of the Electron.- 6.5 Wave Character of Electrons.- Problems.- 7. Some Basic Properties of Matter Waves.- 7.1 Wave Packets.- 7.2 Probabilistic Interpretation.- 7.3 The Heisenberg Uncertainty Relation.- 7.4 The Energy-Time Uncertainty Relation.- 7.5 Some Consequences of the Uncertainty Relations for Bound States.- Problems.- 8. Bohr's Model of the Hydrogen Atom.- 8.1 Basic Principles of Spectroscopy.- 8.2 The Optical Spectrum of the Hydrogen Atom.- 8.3 Bohr's Postulates.- 8.4 Some Quantitative Conclusions.- 8.5 Motion of the Nucleus.- 8.6 Spectra of Hydrogen-like Atoms.- 8.7 Muonic Atoms.- 8.8 Excitation of Quantum Jumps by Collisions.- 8.9 Sommerfeld's Extension of the Bohr Model and the Experimental Justification of a Second Quantum Number.- 8.10 Lifting of Orbital Degeneracy by the Relativistic Mass Change.- 8.11 Limits of the Bohr-Sommerfeld Theory. The Correspondence Principle.- 8.12 Rydberg Atoms.- Problems.- 9. The Mathematical Framework of Quantum Theory.- 9.1 The Particle in a Box.- 9.2 The Schrodinger Equation.- 9.3 The Conceptual Basis of Quantum Theory.- 9.3.1 Observations, Values of Measurements and Operators.- 9.3.2 Momentum Measurement and Momentum Probability.- 9.3.3 Average Values and Expectation Values.- 9.3.4 Operators and Expectation Values.- 9.3.5 Equations for Determining the Wavefunction.- 9.3.6 Simultaneous Observability and Commutation Relations.- 9.4 The Quantum Mechanical Oscillator.- Problems.- 10. Quantum Mechanics of the Hydrogen Atom.- 10.1 Motion in a Central Field.- 10.2 Angular Momentum Eigenfunctions.- 10.3 The Radial Wavefunctions in a Central Field *.- 10.4 The Radial Wavefunctions of Hydrogen.- Problems.- 11. Lifting of the Orbital Degeneracy in the Spectra of Alkali Atoms.- 11.1 Shell Structure.- 11.2 Screening.- 11.3 The Term Diagram.- 11.4 Inner Shells.- Problems.- 12. Orbital and Spin Magnetism. Fine Structure.- 12.1 Introduction and Overview.- 12.2 Magnetic Moment of the Orbital Motion.- 12.3 Precession and Orientation in a Magnetic Field.- 12.4 Spin and Magnetic Moment of the Electron.- 12.5 Determination of the Gyromagnetic Ratio by the Einstein-de Haas Method.- 12.6 Detection of Directional Quantisation by Stern and Gerlach.- 12.7 Fine Structure and Spin-Orbit Coupling: Overview.- 12.8 Calculation of Spin-Orbit Splitting in the Bohr Model.- 12.9 Level Scheme of the Alkali Atoms.- 12.10 Fine Structure in the Hydrogen Atom.- 12.11 The Lamb Shift.- Problems.- 13. Atoms in a Magnetic Field: Experiments and Their Semiclassical Description.- 13.1 Directional Quantisation in a Magnetic Field.- 13.2 Electron Spin Resonance.- 13.3 The Zeeman Effect.- 13.3.1 Experiments.- 13.3.2 Explanation of the Zeeman Effect from the Standpoint of Classical Electron Theory.- 13.3.3 Description of the Ordinary Zeeman Effect by the Vector Model.- 13.3.4 The Anomalous Zeeman Effect.- 13.3.5 Magnetic Moments with Spin-Orbit Coupling.- 13.3.6 The Paschen-Back Effect.- 13.3.7 Double Resonance and Optical Pumping.- Problems.- 14. Atoms in a Magnetic Field: Quantum Mechanical Treatment.- 14.1 Quantum Theory of the Ordinary Zeeman Effect.- 14.2 Quantum Theoretical Treatment of the Electron and Proton Spins.- 14.2.1 Spin as Angular Momentum.- 14.2.2 Spin Operators, Spin Matrices and Spin Wavefunctions.- 14.2.3 The Schrodinger Equation of a Spin in a Magnetic Field.- 14.2.4 Description of Spin Precession by Expectation Values.- 14.3 Quantum Mechanical Treatment of the Anomalous Zeeman Effect with Spin-Orbit Coupling.- 14.4 Quantum Theory of a Spin in Mutually Perpendicular Magnetic Fields, One Constant and One Time Dependent.- 14.5 The Bloch Equations.- Problem.- 15. Atoms in an Electric Field.- 15.1 Observations of the Stark Effect.- 15.2 Quantum Theory of the Linear and Quadratic Stark Effects.- 15.2.1 TheHamiltonian.- 15.2.2 The Quadratic Stark Effect. Perturbation Theory Without Degeneracy.- 15.2.3 The Linear Stark Effect. Perturbation Theory in the Presence of Degeneracy.- 15.3 The Interaction of a Two-Level Atom with a Coherent Radiation Field.- 15.4 Spin-and Photon Echoes.- Problems.- 16. General Laws of Optical Transitions.- 16.1 Symmetries and Selection Rules.- 16.1.1 Optical Matrix Elements.- 16.1.2 Examples of the Symmetry Behaviour of Wavefunctions.- 16.1.3 Selection Rules.- 16.1.4 Selection Rules and Multipole Radiation.- 16.2 Linewidths and Lineshapes.- 17. Many-Electron Atoms.- 17.1 The Spectrum of the Helium Atom.- 17.2 Electron Repulsion and the Pauli Principle.- 17.3 Angular Momentum Coupling.- 17.3.1 Coupling Mechanism.- 17.3.2 …