The status of research in the Physics of Highly Excited Atoms and Ions is covered in this monograph. It includes today's approaches and methods for describing isolated Rydberg atoms and ions, radiative transitions between highly excited states, and photoionization and photorecombination processes. The authors present a number of efficient methods for the calculations in the theory of collisions of highly excited atoms and ions with neutral and charged particles and of spectral-line broadening of Rydberg atomic series in gases, low- and high-temperature plasmas, and astrophysics. Particular attention is paid to a comparison of the theoretical results with available experimental data.

1. Introduction.- 1.1 Physical Properties and Features of Rydberg Atoms and Ions.- 1.2 Scope of the Book.- 2. Classical and Quantum Description of Rydberg Atom.- 2.1 Classical Motion in a Coulomb Field.- 2.2 Wave Functions: Coordinate Representation.- 2.3 Wave Functions: Momentum Representation.- 2.4 Density Matrix and Distribution Function.- 3. Radiative Transitions and Form Factors.- 3.1 Probabilities of Radiative Transitions.- 3.2 Photoionization and Photorecombination.- 3.3 Transition Form Factors.- 4. Basic Approaches to Collisions Involving Highly Excited Atoms and Ions.- 4.1 Formulation of Problem.- 4.2 Born Approximation: Momentum Representation.- 4.3 Time-Dependent Approach: Impact-Parameter Representation.- 4.4 Semiclassical Approach in Action Variables.- 4.5 Impulse Approximation Approach.- 5. Collisions of Rydberg Atom with Neutral Particles: Weak-Coupling Models.- 5.1 Quasi-free Electron Model.- 5.2 Scattering of Ultra-Slow Electrons by Atoms and Molecules.- 5.3 Semiclassical Theory: Impact-Parameter Approach with Fermi Pseudopotential.- 5.4 Impulse Approximation for Rydberg Atom-Neutral Collisions.- 6. Elementary Processes Involving Rydberg Atoms and Neutral Particles: Effects of Electron-Projectile Interaction.- 6.1 Classification of Processes and Theoretical Treatments.- 6.2 Transitions between the Fine-Structure Components and Elastic Scattering.- 6.3 Orbital Angular Momentum and Energy Transfer: l-Mixing and n, l-Changing Processes.- 6.4 Ionization of Rydberg Atom by Atomic Projectile.- 6.5 Quenching of Rydberg States: Thermal Collisions with Atoms.- 6.6 Quenching and Ionization of Rydberg States: Thermal Collisions with Molecules.- 7. Effects of Ion Core in Rydberg Atom-Neutral Collisions.- 7.1 Mechanisms of Perturber-Core Scattering.- 7.2 Separated-Atoms Approach: Shake-Up Model.- 7.3 Quasi-molecular Approach: Basic Assumptions.- 7.4 Exchange of Rydberg Electron Energy with Translational Motion of Atoms.- 7.5 Resonant Excitation and Ionization.- 8. Inelastic Transitions Induced by Collisions of Rydberg Atom (Ion) with Charged Particles.- 8.1 Basic Problems.- 8.2 n-Changing Transitions.- 8.3 l-Changing Transitions.- 9. Spectral-Line Broadening and Shift.- 9.1 Classical and Quantum Treatments of Impact Broadening.- 9.2 Theory of Width and Shift of Rydberg Levels in Gas.- 9.3 Comparison of Theory with Experiment.- 9.4 Broadening of n - n? Lines in a Plasma.- List of Symbols.- References.