Preface

From August 26 till September 1, 2002 the ancient college of The Falcon in Leuven was the scene of the sixteenth edition of the International Jahn–Teller conference. This series of meetings started in Bad Honnef in 1976, first as an annual symposium, later on since 1983 as a biannual international conference. Conference locations alternated between Western and Eastern Europe, but in 2000 the conference moved to Boston, to come back to Europe now and find hospitality at the Catholic University of Leuven, Belgium. Over the years the theme of the conference has broadened to cover all aspects and possible manifestations of vibronic interactions. In this evolution the Jahn–Teller effect itself acts as a kind of paradigmatic core, describing the symmetric case of electronic degeneracy. In the conference in Leuven, the whole spectrum of applications in chemistry and physics was amply demonstrated through 12 invited plenary lectures, 25 oral presentations, and some 40 posters. The present volume offers a detailed account of all this work.

In spite of the long history of the Jahn–Teller effect new fundamental perspectives were also presented at this sixteenth edition: they were in part inspired by the developing studies of icosahedral systems, mainly in fullerene science, which require advanced group theoretical and topological techniques. One of the important fundamental themes during the conference was the theoretical description of nonadiabatic effects. Strong debates were held over the role of the geometric phase in connection with the topology of the seam of conical intersections. Participants left the conference with the idea that serious further work must be done on the clarification of the nonadiabatic effect. There should come an unambiguous answer to the question of how to describe the dynamics in the crossing region of two adiabatic potential energy surfaces. From the chemical point of view we discovered the firm statement that so far detailed analysis of some twenty photochemical processes has revealed that the photochemical reaction always proceeds through a conical intersection. This aspect has important consequences both for the study of chemical reactions and the role of Woodward-Hoffmann selection rules, and for the study of the Jahn–Teller effect itself. We hope that these two lines of research will converge towards each other in the near future. Traditionally the Jahn–Teller effect in physics is connected to the study of impurity centres and cooperative phenomena in the solid state, and the current proceedings contains accounts of several new developments in this area. One new aspect involves the concept of an ‘orbiton’, an orbital excitation in a lattice which can travel as a wave, and may couple to Jahn–Teller active vibrations and to spin magnons. Fullerenes and the hot topic of their potential xxiii superconductivity in positively charged states mark another area of continuing emphasis, where the Jahn–Teller effect is prominently present in current physics.

We hope that the participants and the larger scientific community, interested in vibronic effect, may find in the present volume a reference text on the current status of the study of the Jahn–Teller effect, and a source of inspiration for future work.At the end we express our profound gratitude to the conference secretary, Mrs. R. Jungbluth-Hendrickx, for the perfect organisation, to the international organizing committee, chaired by Prof. Colin Bates for the full support with the programme, and to our sponsors: K.U. Leuven, the research community of the Flemish Quantum Chemists, and the National Science Fund, F.W.O. Vlaanderen.

While the proceedings of the sixteenth conference went into press, news agencies around the world announced the decease of Dr. Edward Teller at the age of 95. The Jahn–Teller community commemorates him as author, together with Jahn, of the seminal paper that gave birth to the entire subject of symmetry breaking and vibronic coupling.

Arnout CEULEMANS, Liviu CHIBOTARU, Eugene KRYACHKO

Division of Quantum Chemistry, K.U. Leuven,

Celestijnenlaan 200F, B-3001 Leuven, Belgium

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