PB and AsB triple bonds in the linear PB2O− and AsB2O− species

Abstract

Due to its electron deficiency, boron triple bonds are relatively scarce. We use high-resolution photoelectron imaging to investigate the structures and bonding of the EB₂O⁻ (E = P, As) type of clusters, which are found to have [EB–BO]⁻ closed-shell linear structures with EB triple bonds. The B atoms in the linear EB₂O⁻ species undergo sp hybridization, while the E atoms also undergo sp hybridization to form a σ bond with the sp orbital of B along with two π bonds formed by the p_x and p_y orbitals. The high-resolution photoelectron imaging data reveal detachment transitions from the EB₂O⁻ (¹Σ⁺) anions to the EB₂O (²Π) neutrals. The electron affinities of PB₂O and AsB₂O are measured to be 3.592(1) eV and 3.432(1) eV, respectively; the vibrational frequencies for the E–B, B–B, and B–O stretching modes are measured for both species. The spin–orbit splitting of the ²Π state to ²Π_3/2 and ²Π_1/2 is measured to be 153 cm⁻¹ and 758 cm⁻¹ for PB₂O and AsB₂O, respectively.