Conical intersection research

Oosterhoff correlation diagram, conical intersection research, 494-496... 

The nature of the Cl has been a subject of research for at least three decades. Between 1966 and 1972, Zimmerman, Michl and Salem [9-14] were the first to propose, independently, that for a broad class of organic reactions the structure of the funnel could be determined by locating a cone shaped crossing of the excited and ground state (potential) energy surfaces, known as conical intersection. More recently, Yarkony [15-17] and Ruendenberg [18] identified conical intersections geometries in small molecules. 

The calculation of excitation energies and transition moments for unsaturated organic molecules has been one of the more successful applications of multiconhgurational quantum chemistry since the hrst application to the benzene molecule in 1992 [34]. Many hundred molecules have been studied. The CASSCF method allows optimization of excited state energy surfaces and this has been used to compute vibrationally resolved electronic spectra [35,36]. The method is used by several research groups for studies of photochemical reactions, including the localization of conical intersections, etc. 

The aim of the present section is to supplement the discussions of the Born-Oppenheimer approximation and of conical intersections presented in this book. In particular, we would like to briefly discuss three subjects the presence of external fields, nonstationary electronic states, and the role of molecular rotations in conical intersection situations. Each of these subjects presents by itself a large area of research and would deserve a detailed account. Here, we shall only touch upon these subjects without going into any details. 

We have considered a large number of issues concerning conical intersections. Several interesting issues have not been discussed. Here we briefly mention these topics and suggest directions for future research. 

On the other hand, the importance of the progress in this field has been recently reckoned by the European Commission for the Research. Very obviously, the knowledge of conical intersections appears to be a key step for the rational design of molecules capable to either exploit or waste the photon energy (see for instance Ref. 38). 

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