GROUP-VI TRIMERS (SE-3, TE-3, AND PO-3) - ELECTRONIC STATES AND POTENTIAL-ENERGY SURFACES

The potential energy surfaces of several electronic states of Se3, Te3, and Po3 are computed. We employed the ab initio complete active space multiconfiguration self-consistent field followed by multireference configuration interaction techniques which included up to 1.7 million configurations. Our computations reveal two nearly degenerate electronic states with D3h(1A1') and C2v(1A1) symmetries as candidates for the ground states, although the C2v minimum was found to be favored at the highest level of theory. Our computations facilitate the assignment of the observed spectra of Se3 and Te3 in the visible region by Andrews and co-workers to the B-1(2)-X1 A1 systems. Our computed T(e) values were found to be in excellent agreement with experiment. We computed the dipole moments, dissociation and atomization energies for all three trimers and the vertical ionization energies for the two minima of Se3. The analysis of the periodic trends revealed significant relativistic effects for Po3.