P[triple bond, length as m-dash]B and As[triple bond, length as m-dash]B triple bonds in the linear PBO and AsBO 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 the EBO (E = P, As) type of clusters, which are found to have [E[triple bond, length as m-dash]B-B[triple bond, length as m-dash]O] closed-shell linear structures with E[triple bond, length as m-dash]B triple bonds. The B atoms in the linear EBO 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 and p orbitals. The high-resolution photoelectron imaging data reveal detachment transitions from the EBO (Σ) anions to the EBO (Π) neutrals. The electron affinities of PBO and AsBO 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 Π state to Π and Π is measured to be 153 cm and 758 cm for PBO and AsBO, respectively.