VIOLATION OF THE WEAK NONCROSSING RULE BETWEEN TOTALLY SYMMETRICAL CLOSED-SHELL STATES IN THE VALENCE-ISOELECTRONIC SERIES O-3, S-3, SO2, AND S2O

The ground and next excited (1)A(1) potential energy surfaces of the v alence-isoelectronic molecules O-3, S-3, SO2, and S2O have been studie d using full-valence-space-multiconfiguration self-consistent-field ca lculations. An open and a ring minimum were found for all species. In each case, interconversion between the C-2v open and closed isomers pr oceeds via a C-2v transition state which lies on a very sharp ridge se parating the basins surrounding the minima. In the immediate vicinity of these transition states, the upper state for each species is found to have a minimum, also in C-2v. Furthermore, not far away on the C-2v ridges, the 1 (1)A(1) and 2 (1)A(1) surfaces intersect conically for all molecules. (C) 1997 American Institute of Physics.