Unusual conical intersections in the Jahn–Teller effect: The electronically excited states of Li3

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Abstract
Conical intersections of the 2 2 E ′ and 1 2 A 1 ′ states of Li 3 are considered as a first step in the description of the excited state involved in the absorption at 14 583 cm−1. Quite novel results are obtained. In addition to the standard symmetry-required D 3h seam of conical intersection, C 2v symmetry-allowed seams are found and their locus determined as a function the symmetric stretch coordinate. The C 2v seams of conical intersection intersect the D 3h conical intersection seam at two distinct points producing two heptafurcations of the D 3h seam. The locus of the C 2v conical intersection points is explained in terms of a quadratic Jahn–Teller model. The overall geometric phase effect associated with the D 3h and C 2v conical intersections is well described using a previously suggested phase factor deduced from molecular properties. In addition to these conical intersections an intersection of the 1 2 A 1 ′ and 2 2 E ′ is states is located.