SADDLE STRUCTURE OF THE 3-BODY COULOMB PROBLEM - SYMMETRIES OF DOUBLY-EXCITED STATES AND PROPENSITY RULES FOR TRANSITIONS

The separable two-centre Coulomb problem is investigated with emphasis on the saddle structure of its potential. A new quasi-degeneracy between molecular orbitals (MO) is identified. We demonstrate that the results have threefold relevance for the formation and character of symmetric doubly-excited states: (i) it is shown that all features of Herrick's various multiplet classifications can be explained in terms of MO saddle dynamics; (ii) for the first time quantitative results of resonance energies from the adiabatic MO approach are reported and compared to other theoretical and experimental data; (iii) the propensity rules for radiative and non-radiative transitions are summarized and details of their derivation within the framework of motion in the vicinity of the potential saddle are given.