Conical intersections three-state molecular system

B. The Study of a Real Three-State Molecular System Strongly Coupled (2,3) and (3,4) Conical Intersections... 

Longuet-Higgins phase-based treatment, two-dimensional two-surface system, scattering calculation, 154-155 three-state molecular system, 134-137 two-state molecular system, single conical intersection solution, 98-101 permutational symmetry, degenerate/near-degenerate vibrational levels, 730-733 Polyene molecules ... 

The discussion so far has focused on two-state conical intersections, which are the most common conical intersections, and which have been studied extensively. Three-state degeneracies imposed by symmetry have been studied in the context of the Jahn-Teller problem for many decades,but only minor attention had been given to accidental three-state degeneracies in molecules until recently. As most molecular systems in nature have low or no symmetry, these accidental intersections may have a great impact on the photophysics and photochemistry of those molecular systems, as has been found in accidental two-state intersections.Three-state degeneracies may provide a more efficient relaxation pathway when more than one interstate transition is needed. Moreover, they introduce more complicated geometric phase effects,and they can affect the system s dynamics and pathways available for radiationless transitions. 

Abstract In this article we present a survey of the various conical intersections which govern potential transitions between the three lower electronic states for the title molecular system. It was revealed that these three states, for a given fixed HH distanee, Rhhj usually form four conical intersections two between the two lower states and two between the two upper states. One of the four is the well-known equilateral Dsh ci and the others are, essentially, C2V cis One of them is located on the symmetry line perpendicular to the HH axis (like the Dsh ci) and the other two are located on both sides of this symmetry line and in this way form the twin C2V cis. The study was carried out for two Rnn-values, namely, Rhh O.74 and 0.4777 A. 

Two-state conical intersections have been well established in many types of molecular systems. In contrast, the study of three-state conical intersections is still in its infancy, and detailed studies are needed to understand the influence of these intersections on the dynamical behavior of molecules. 

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