Atoms And Molecules In Strong External Fields

This book contains contributions to the 172. WE-Heraeus-Seminar “Atoms and Molecules in Strong External Fields,” which took place April 7–11 1997 at the Phys- zentrum Bad Honnef (Germany). The designation “strong fields” applies to external static magnetic, and/or electric fields that are sufficiently intense to cause alterations in the atomic or molecular str- ture and dynamics. The specific topics treated are the behavior and properties of atoms in strong static fields, the fundamental aspects and electronic structure of molecules in strong magnetic fields, the dynamics and aspects of chaos in highly excited R- berg atoms in external fields, matter in the atmosphere of astrophysical objects (white dwarfs, neutron stars), and quantum nanostructures in strong magnetic fields. It is obvious that the elaboration of the corresponding properties in these regimes causes the greatest difficulties, and is incomplete even today. Present-day technology has made it possible for many research groups to study the behavior of matter in strong external fields, both experimentally and theore- cally, where the phrase “experimentally” includes the astronomical observations. - derstanding these systems requires the development of modern theories and powerful computational techniques. Interdisciplinary collaborations will be helpful and useful in developing more efficient methods to understand these important systems. Hence the idea was to bring together people from different fields like atomic and molecular physics, theoretical chemistry, astrophysics and all those colleagues interested in aspects of few-body systems in external fields.

Atoms and Molecules describes the basic properties of atoms and molecules in terms of group theoretical methods in atomic and molecular physics. The book reviews mathematical concepts related to angular momentum properties, finite and continuous rotation groups, tensor operators, the Wigner-Eckart theorem, vector fields, and vector spherical harmonics. The text also explains quantum mechanics, including symmetry considerations, second quantization, density matrices, time-dependent, and time-independent approximation methods. The book explains atomic structure, particularly the Dirac equation in which its nonrelativistic approximation provides the basis for the derivation of the Hamiltonians for all important interactions, such as spin-orbit, external fields, hyperfine. Along with multielectron atoms, the text discusses multiplet theory, the Hartree-Fock formulation, as well as the electromagnetic radiation fields, their interactions with atoms in first and higher orders. The book explores molecules and complexes, including the Born-Oppenheimer approximation, molecular orbitals, the self-consistent field method, electronic states, vibrational and rotational states, molecular spectra, and the ligand field theory. The book can prove useful for graduate or advanced students and academicians in the field of general and applied physics.

This book collects the lectures given at the NATO Advanced Study Institute on "Atoms in Strong Fields", which took place on the island of Kos, Greece, during the two weeks of October 9-21,1988. The designation "strong field" applies here to an external electromagnetic field that is sufficiently strong to cause highly nonlinear alterations in atomic or molecular struc ture and dynamics. The specific topics treated in this volume fall into two general cater gories, which are those for which strong field effects can be studied in detail in terrestrial laboratories: the dynamics of excited states in static or quasi-static electric and magnetic fields; and the interaction of atoms and molecules with intense laser radiation. In both areas there exist promising opportunities for research of a fundamental nature. An electric field of even a few volts per centimeter can be very strong on the atom ic scale, if it acts upon a weakly bound state. The study of Rydberg states with high reso lution laser spectroscopic techniques has made it possible to follow the transition from weak-field to strong-field behavior in remarkable detail, using static fields of modest lab oratory strength; in the course of this transition the atomic system evolves from one which can be thoroughly understood in terms of field-free quantum numbers, to one which cannot be meaningfully associated at all with the zero-field states of the atom.

This book draws together the principal ideas that form the basis of atomic, molecular, and optical science and engineering. It covers the basics of atoms, diatomic molecules, atoms and molecules in static and electromagnetic fields and nonlinear optics. Exercises and bibliographies supplement each chapter, while several appendices present such important background information as physics and math definitions, atomic and molecular data, and tensor algebra. Accessible to advanced undergraduates, graduate students, or researchers who have been trained in one of the conventional curricula of physics, chemistry, or engineering but who need to acquire familiarity with adjacent areas in order to pursue their research goals.

The recent evolution of lasers and other external field (e.g. Synchrotron radiation, strong electric and magnetic fields) sources is opening up new frontiers of science which cover explorations in broad areas ranging from atomic, molecular and optical physics (AMOP) to nuclear fusion and high energy particle physics; even further to astrophysics and cosmology. Atomic and molecular dynamics is being explored at the femto and near atto- second time scale. Ultra-intense laser and other external fields attracting vigorous attention and interest from the view point of their control. The topics covered in the book are: Applications of ultra-intense ultra-short pulse lasers; Atoms, molecules and clusters in strong laser and other external fields; high field chemistry; high harmonic generation (HHG), X-ray generation by laser matter interactions and their applications, collisions in laser fields, relativistic particle generation and acceleration by super-strong laser plasma interactions etc.

In this thesis, the ionization of atoms and small molecules in strong laser fields is experimentally studied using a reaction microscope. The population of autoionizing doubly excited states in the laser fields is proven and a possible connection to the well-known dielectronic recombination processes is discussed. The fundamental process of tunnel ionization in strong laser fields is subject of investigation in a pump-probe experiment with ultrashort laser pulses. A coherent superposition of electronic states in singly charged argon ions is created within the first, and subsequently tunnel-ionized with the second pulse. This gives access to state-selective information about the tunneling process and allows to test common models. Moreover, the ionization of krypton and argon at different wavelengths is studied, from the multiphoton to the tunneling regime. The wavelength-dependent investigations are furthermore extended to molecular hydrogen. In addition to ionization, this system might undergo different dissociative processes. Channel-selective electron momentum distributions are presented and compared to each other.

Originally published as part of the renowned Bergmann-Schaefer textbook series on experimental physics, this volume fills an important void by providing a thorough treatment of the basic: atoms, molecules, nuclei, and particles. Written by experimentalists, it forms a unique compendium of our practical knowledge of the basic elements While keeping all of the rigor necessary for a clean treatment, the authors go beyond theory and describe major experimental results that give readers a clear view of the practical side of nature.

This volume offers theoretical investigations of atoms and molecules interacting with pulsed or continuous wave lasers. Theoretical background is included, and the text incorporates several exercises. Additional calculations are performed in the appendices.