P[triple bond, length as m-dash]B and As[triple bond, length as m-dash]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 the EB2O- (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 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 2Π3/2 and 2Π1/2 is measured to be 153 cm-1 and 758 cm-1 for PB2O and AsB2O, respectively.