Photoelectron Spectroscopy of BiAu(-) and BiBO(-): Further Evidence of the Analogy between Au and Boronyl.

Boronyl (BO) is a monovalent σ radical with a B≡O triple bond. Its chemistry has remained relatively unknown, though analogy has been established for BO with monovalent atoms, such as H or Au. Here we report a photoelectron spectroscopic study of BiAu(-) and BiBO(-), showing further evidence of the analogy between Au and BO. The photoelectron spectra of BiAu(-) and BiBO(-) are found to be similar, suggesting that they possess similar electronic structure and chemical bonding. The electron affinities of BiAu and BiBO are measured to be 1.38(4) and 1.84(3) eV, respectively. The ground states of both BiAu and BiBO are shown to be a triplet (X (3)Σ(-)). In addition, vibrational structures are resolved in the spectra of BiBO(-). Two vibrational frequencies at 320(30) and 1860(50) cm(-1) are measured for the ground state of BiBO, corresponding to the Bi-B and B-O stretching modes, respectively. The low-lying electronic excited states of BiAu and BiBO are also found to be similar: their first four excited states are A (1)Δ, B (1)Σ(+), C (3)Π, and D (1)Π, with excitation energies at 0.71, 1.29, 2.54, and 2.67 eV for BiAu and 0.63, 1.26, 3.68, and 3.82 eV for BiBO, respectively, above the (3)Σ(-) ground state. Weak photoelectron features related to two-electron detachment transitions are also observed for both anions because of strong electron correlation effects in the ground state of the anions.