The concept of adiabatic electronic potential-energy surfaces, defined by the Born-Oppenheimer approximation, is fundamental to our thinking about chemical processes. Recent computational as well as experimental studies have produced ample evidence that the so-called conical intersections of electronic energy surfaces, predicted by von Neumann and Wigner in 1929, are the rule rather than the exception in polyatomic molecules. It is nowadays increasingly recognized that conical intersections play a key mechanistic role in chemical reaction dynamics. This volume provides an up-to-date overview of the multi-faceted research on the role of conical intersections in photochemistry and photobiology, including basic theoretical concepts, novel computational strategies as well as innovative experiments. The contents and discussions will be of value to advanced students and researchers in photochemistry, molecular spectroscopy and related areas.

TheJahn Teller(JT)effectcontinuesto bea paradigmforstructuralinstabilitiesand dynamicalprocessesinmoleculesandin the condensedphase.While thebasic th- rem, rst published in 1937, had to await experimentalveri cation for 15 years, the intervening years saw rapid development, initially in the theoretical arena, followed increasingly by experimental work on molecules and crystals. The International Jahn Teller Symposiumwas established in the mid-1970s, to foster the exchangeof ideas between researchers in the eld. Among the many important developments in the eld, we mention cooperative phenomena in crystals, the general importance of pseudo-Jahn Teller (PJT) couplings for symmetry-lowering phenomena in mol- ular systems, nonadiabatic processes at conical intersections of potential energy surfaces and extensions of the basic theory in relation to the discovery of fullerenes and other icosahedral systems. It is the objectiveof this volume to providethe interested reader with a collection of tutorial reviews by leading researchers in the eld. These reviews provide a c- prehensive overview of the current status of the eld, including important recent developments.This volume is targeted at both the non-expertscientist as well as the expert who wants to expand his/her knowledge in allied areas. It is intended to be a complement to the existing excellent textbooks in the eld. Guided by the idea of tutorial reviews, we provide here short introductoryremarks to the various sections, astheyappearin thetable ofcontents.These arefollowedbya briefcharacterization of the individual papers to make their basic contents, as well as their interrelation, more transparent."