Conical Intersections - Electronic Structure, Dynamics and Spectroscopy

Abstract

INTRODUCTIONMany of us who are involved in teaching a special-topic graduate course may have the experience that it is difficult to find suitable references, especially reference materials put together in a suitable text format. Presently, several excellent book series exist and they have served the scientific community well in reviewing new developments in physical chemistry and chemical physics. However, these existing series publish mostly monographs consisting of review chapters of unrelated subjects. The modern development of theoretical and experimental research has become highly specialized. Even in a small subfield, experimental or theoretical, few reviewers are capable of giving an in-depth review with good balance in various new developments. A thorough and more useful review should consist of chapters written by specialists covering all aspects of the field. This book series is established with these needs in mind. That is, the goal of this series is to publish selected graduate texts and stand-alone review monographs with specific themes, focusing on modern topics and new developments in experimental and theoretical physical chemistry. In review chapters, the authors are encouraged to provide a section on future developments and needs. We hope that the texts and review monographs of this series will be more useful to new researchers about to enter the field. In order to serve a wider graduate student body, the publisher is committed to making available the monographs of the series in a paperbound version as well as the normal hardcover copy. Cheuk-Yiu Ng PREFACEThe Born-Oppenheimer adiabatic approximation represents one of the cornerstones of molecular physics and chemistry. The concept of adiabatic potential-energy surfaces, defined by the Born-Oppenheimer approximation, is fundamental to our thinking about molecular spectroscopy and chemical reaction dynamics. Many chemical processes can be rationalized in terms of the dynamics of the atomic nuclei on a single BornOppenheimer potential-energy surface. Nonadiabatic processes, that is, chemical processes which involve nuclear dynamics on at least two coupled potential-energy surfaces and thus cannot be rationalized within the BornOppenheimer approximation, are nevertheless ubiquitous in chemistry, most notably in photochemistry and photobiology. Typical phenomena associated with a violation of the Born-Oppenheimer approximation are the radiationless relaxation of excited electronic states, photoinduced unimolecular decay and isomerization processes of polyatomic molecules. During the last few decades, we have witnessed a change of paradigms in nonadiabatic chemistry. First, the remarkable advances achieved in femtosecond laser technology and time-resolved spectroscopy have revealed that the radiationless decay of excited electronic states may take place much faster than previously thought. The traditional theory of radiationless decay processes, developed in the sixties and seventies of the last century, cannot explain electronic decay occurring on ...