Systematic location of intersecting seams of conical intersection in triatomic molecules:: The 12A′-22A′ conical intersections in BH2

Points of conical intersection are continuously connected forming seams. Recently a quite unanticipated situation has been found in which two distinct seams of conical intersection-one symmetry-allowed and one same-symmetry-originating from the same two states intersect each other. The identification of these confluences, based on ab initio electronic wave functions has been somewhat serendipitous. A systematic approach for locating such confluences, based solely on information obtained on the symmetry-allowed portion of the seam, has been suggested. In this work that approach is applied to identify the point where a C-s seam of conical intersection intersects a symmetry-allowed C-2v seam of conical intersection for the 1 (2)A' and 2 (2)A' states of BH2, states that correlate with B(1s(2)2s(2)2p,P-2)+ H-2. It is suggested, based on this and previous work, that this unexpected situation, which has fundamental implications for our understanding of nonadiabatic processes, is not at all uncommon. (C) 1998 American Institute of Physics.