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

Conical intersections of the 2 2E′ and 1 2A1′ states of Li3 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 D3h seam of conical intersection, C2v symmetry-allowed seams are found and their locus determined as a function the symmetric stretch coordinate. The C2v seams of conical intersection intersect the D3h conical intersection seam at two distinct points producing two heptafurcations of the D3h seam. The locus of the C2v conical intersection points is explained in terms of a quadratic Jahn–Teller model. The overall geometric phase effect associated with the D3h and C2v 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 2A1′ and 2 2E′ is states is located.