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Advances in Chemistry
Volume 2014 (2014), Article ID 419102, 10 pages
Review Article

Conical Intersections Leading to Chemical Reactions in the Gas and Liquid Phases

Institute of Chemistry, the Hebrew University of Jerusalem, 91904 Jerusalem, Israel

Received 2 July 2014; Revised 9 October 2014; Accepted 13 October 2014; Published 16 November 2014

Academic Editor: Rosendo Valero

Copyright © 2014 Yehuda Haas. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The current status of the role of conical intersections (CoIns) in molecular photochemistry is reviewed with a special emphasis on the procedures used to locate them. Due to space limitations, the extensive literature of the subject is given by referring the reader to representative references, whereas the author group’s work is described in detail. The basic properties of CoIns are outlined and contrasted with those of transition states in thermal reactions. Location of CoIns using the method of Longuet-Higgins sign-inverting loops is described in detail. The concept of “anchors”—valence bond structures that represent stable molecules and other stationary points on the potential energy surface—is introduced and its use in constructing loops is described. The authors’ work in the field is outlined by discussing some specific examples in detail. Mathematical aspects and details are left out. The main significance of the method is that it explains a large body of photochemical reactions (for instance, ultrafast ones) and is particularly suitable for practicing chemists, using concepts such as reaction coordinates and transition states in the search.