Ionization energies and cationic bond dissociation energies of RuB, RhB, OsB, IrB, and PtB.

Two-photon ionization thresholds of RuB, RhB, OsB, IrB, and PtB have been measured using resonant two-photon ionization spectroscopy in a jet-cooled molecular beam and have been used to derive the adiabatic ionization energies of these molecules. From the measured two-photon ionization thresholds, IE(RuB) = 7.879(9) eV, IE(RhB) = 8.234(10) eV, IE(OsB) = 7.955(9) eV, IE(IrB) = 8.301(15) eV, and IE(PtB) = 8.524(10) eV have been assigned. By employing a thermochemical cycle, cationic bond dissociation energies of these molecules have also been derived, giving D(Ru-B) = 4.297(9) eV, D(Rh-B) = 4.477(10) eV, D(Os-B) = 4.721(9) eV, D(Ir-B) = 4.925(18) eV, and D(Pt-B) = 5.009(10) eV. The electronic structures of the resulting cationic transition metal monoborides (MB) have been elucidated using quantum chemical calculations. Periodic trends of the MB molecules and comparisons to their neutral counterparts are discussed. The possibility of quadruple chemical bonds in all of these cationic transition metal monoborides is also discussed.