This book is based mostly on the reports presented at the XVth International lahn-Teller Symposium on Vibronic Interactions in Crystals and Molecules and NATO Advanced Research Workshop Colossal Magnetoresistance and Vibronic Interactions that took place at Boston on August 16-22 of the year 2000. This is the first time the Symposium took place in the USA where recently the giant splash of the attention to the 1 ahn-Teller effect occurred. This tremendous interest to the field all over the world is reflected not only in the numerous publications in many American and European 10urnals, but of the leading scientists from additionally in the Symposium's participation the well known Universities, National Laboratories and industrial companies, which was the largest in the history of the Symposium. The renaissance of the 1ahn-Teller physics is closely related to the three fundamental discoveries in science. The most significant among them is the discovery of high-Tc superconductivity by K. -A. Muller and G. Bednorz, for whom the "1ahn-Teller idea" was the motivation in their search. The result of this search is well known - a wide spectrum of the 1ahn-Teller ion based materials with Tc between 24K and 135K were found. The second discovery is the existence of a new polymorph of carbon - the C60. The microscopic analysis of all physical, chemical and biological properties of the buckyballs is based on 1ahn-Teller type of interactions. The third is colossal magnetoresistance.

This book is based mostly on the reports presented at the XVth International lahn-Teller Symposium on Vibronic Interactions in Crystals and Molecules and NATO Advanced Research Workshop Colossal Magnetoresistance and Vibronic Interactions that took place at Boston on August 16-22 of the year 2000. This is the first time the Symposium took place in the USA where recently the giant splash of the attention to the 1 ahn-Teller effect occurred. This tremendous interest to the field all over the world is reflected not only in the numerous publications in many American and European 10urnals, but of the leading scientists from additionally in the Symposium's participation the well known Universities, National Laboratories and industrial companies, which was the largest in the history of the Symposium. The renaissance of the 1ahn-Teller physics is closely related to the three fundamental discoveries in science. The most significant among them is the discovery of high-Tc superconductivity by K. -A. Muller and G. Bednorz, for whom the "1ahn-Teller idea" was the motivation in their search. The result of this search is well known - a wide spectrum of the 1ahn-Teller ion based materials with Tc between 24K and 135K were found. The second discovery is the existence of a new polymorph of carbon - the C60. The microscopic analysis of all physical, chemical and biological properties of the buckyballs is based on 1ahn-Teller type of interactions. The third is colossal magnetoresistance.

Vibronic interaction effects constitute a new field of investigation in the physics and chemistry of molecules and crystals that combines all the phenomena and laws originating from the mixing of different electronic states by nuclear displacements. This field is based on a new concept which goes beyond the separate descriptions of electronic and nuclear motions in the adiabatic approximation. Publications on this topic often appear under the title of the lahn-Thller effect, although the area of application of the new approach is much wider: the term vibronic interaction seems to be more appropriate to the field as a whole. The present understanding of the subject was reached only recently, during the last quarter of a century. As a result of intensive development of the theory and experiment, it was shown that the nonadiabatic mixing of close-in-energy elec tronic states under nuclear displacements and the back influence of the modified electronic structure on the nuclear dynamics result in a series of new effects in the properties of molecules and crystals. The applications of the theory of vibronic in of spectroscopy [including visible, ultraviolet, in teractions cover the full range frared, Raman, EPR, NMR, nuclear quadrupole resonance (NQR), nuclear gam ma resonance (NOR), photoelectron and x-ray spectroscopy], polarizability and magnetic susceptibility, scattering phenomena, ideal and impurity crystal physics and chemistry (including structural as well as ferroelectric phase transitions), stereochemistry and instability of molecular (including biological) systems, mechanisms of chemical reactions and catalysis.

The first half of the title of this book may delude the uninitiated reader. The term '"Jahn-Teller effect," taken literally, refers to a special effect inherent in particular molecular systems. Actually, this term implies a new approach to the general problem of correlations between the structure and properties of any molecular polyatomic system, including solids. Just such a new approach, or concept (in some sense, a new outlook or even a new way of thinking), which leads not to one special effect but to a series of different effects and laws, is embodied in the many ( ~ 4000) studies devoted to the investigation and application of the Jahn-Teller effect. The term "vibronic interactions" seems to be most appropriate to the new concept, and this explains the origin of the second half of the title. The primary objective of this book is to present a systematic develop ment of the concept of vibronic interactions and its applications, and to illustrate its possibilities and significance in modern chemistry. In the first three chapters (covering about one-third of the book) the theoretical background of the vibronic concept and Jahn-Teller effect is given. The basic ideas are illustrated fully, although a comprehensive presentation of the theory with all related mathematical deductions is beyond the scope of this book. In the last three chapters the applications of theory to spectro scopy, stereochemistry and crystal chemistry, reactivity, and catalysis, are illustrated by a series of effects and laws.

The concepts of the Jahn-Teller effect and vibronic coupling are being applied to more and more systems in both chemistry and physics. Aspects of structural chemistry such as the distortion of the nuclear framework to a lower-symmetry conformation have received an increasing attention, as well as the dynamics on the coupled potential energy surfaces. The Jahn-Teller intersections are now recognized as prototype cases of conical intersections where the nuclear motion is known to be inherently nonadiabatic in nature and interchanges freely between the different potential energy surfaces. In the condensed phase especially, the significance of the Jahn-Teller effect has been increasingly appreciated, following the discovery of superconductivity in the fullerides and of very large ("colossal") magnetoresistance in the manganite perovskites. Indeed, these materials are particularly challenging since the Jahn-Teller interaction competes with electronic correlation effects. Vibronic Interactions and the Jahn-Teller Effect: Theory and Applications provides an in-depth discussion of the Jahn-Teller effect and vibronic interactions as reflected by the contributions presented at the XX International Conference on the Jahn-Teller effect, Fribourg, Switzerland, 2010. The following topics have been treated in a clear and concise way: • Complex topologies of Jahn-Teller effect and conical intersections • Multi-state vibronic interactions on strongly coupled potential energy surfaces • Interplay of vibronic and spin-orbit coupling • Strain in Jahn-Teller systems and cooperative Jahn-Teller effect • Orbital ordering and its relation to ferromagnetism, ferroelectricity and molecular magnets • The Jahn-Teller effect in icosahedral systems • The Jahn-Teller effect and high temperature superconductivity This book is of interest to a wide audience including academic and industrial theoretical and experimental physicists, chemists, spectroscopists, and crystallographers.