Electronic energies, geometries, and vibrational frequencies of the ground and low-lying excited states of the boron trimer

Ab initio electronic structure calculations on several low-lying valence states of B, have been carried out using correlation-consistent polarized valence double-zeta basis sets and completeactive-space self-consistent field treatments of electron correlation. Stable triangular structures, linear structures, and Jahn-Teller unstable structures are all observed. Equilibrium geometries, energies, and local harmonic vibrational frequencies are determined for various locally stable structures of several states. Several of the local minima are found to be unstable or metastable when zero-point vibrational energy is included; as a result, fluxional species are predicted to occur for certain B, states. Transition states connecting local minima are found and characterized in terrns of energies, geometries, and local harmonic vibrational frequencies. The ground state of B, is predicted to have an equilateral triangular structure and to be of 2A { symmetry in the Dxh point group. Dipole and vibronically allowed vertical transition energies to other states are also considered.