Characterization of the [Xtilde] 1Σ+Ã3Π and Ã1Π electronic states of BBO

The three lowest-lying electronic states, [Xtilde] 1Σ+, A 3II and A 1II, of the linear BBO molecule have been systematically investigated using ab initio electronic structure theory. The equilibrium structures and physical properties including dipole moments, vibrational frequencies and associated infrared intensities, Renner parameters and energetics for the three states of BBO have been determined employing SCF, CISD, CCSD and CCSD(T) levels of theory and a wide range of basis sets. The ground state of BBO presents a degenerate real bending frequency, while the A 3II and A 1II states show two distinct real bending frequencies due to the Renner-Teller interaction. The bending motion of the A 1II state was analysed using the equation-of-motion (EOM)-CCSD and EOM-CC3 techniques in order to avoid possible variational collapse to a lower-lying state. The [Xtilde] 1Σ+-A 3II separation was predicted to be T 0 = 16.6 kcal mol−1 (5800 cm−1, 0.719 eV) at the cc-pVQZ CCSD(T) level of theory. With the cc-pVQZ EOM-C...