P≡B and As≡B Triple Bonds in the Linear PB2O− and AsB2O− Species

Due to its electron deficiency, boron triple bonds are relatively scarce. We use high-resolution photoelectron imaging to investigate the structures and bonding of EB₂O⁻ (E = P, As) type of clusters, which are found to have [E≡B−B≡O]⁻ closed-shell linear structures with E≡B triple bonds. The B atoms in the linear EB₂O⁻ species undergo sp hybridization, while the E atoms also undergo sp hybridization to form a s bond with the sp orbital of B along with two p bonds formed by the p_xand p_y orbitals. The high-resolution photoelectron imaging data reveal detachment transitions from the EB₂O⁻ (¹S⁺) anions to the EB₂O (²P) 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 systems. The spin-orbit splitting of the ²P state to ²P_3/2 and ²P_1/2 is measured to be 153 cm^-1 and 758 cm^-1 for PB₂O and AsB₂O, respectively.