Bond Energy of IrO+: Guided Ion-Beam and Theoretical Studies of the Reaction of Ir+ (5F) with O2

Abstract

The kinetic-energy dependence of the Ir(+) + O2 reaction is examined using guided ion-beam mass spectrometry. The cross section for IrO(+) formation from ground state Ir(+)((5)F) is unusual, and several means are used to interpret the kinetic energy dependence for IrO(+) formation. In analogy with recent observations for the analogous Re(+) and Os(+) systems, we believe the cross section is most accurately analyzed assuming there are two features. This analysis yields a threshold leading to D0(Ir(+)-O) = 4.26 ± 0.09 eV, with the higher energy feature having a threshold 0.72 ± 0.25 eV higher in energy. This bond energy, which is consistent with much less precise values determined in the literature, can be combined with literature information to suggest that D0(IrO) = 4.25 ± 0.44 eV and IE(IrO) = 8.96 ± 0.45 eV. The nature of the bonding for IrO(+) and IrO2(+) is discussed and analyzed primarily using theoretical calculations at the B3LYP/def2-TZVPPD level of theory. Bond energies for ground state IrO(+), identified as (5)Δ, are calculated at this level as well as BP86 and CCSD(T,full) levels using several different basis sets. BP86 theoretical bond energies are higher than the experimental value, whereas B3LYP and CCSD(T,full) values are slightly lower, especially after estimated spin-orbit corrections. Potential energy surfaces for the reaction of Ir(+) with O2 are also calculated at the B3LYP/def2-TZVPPD level of theory and reveal that ground state Ir(+)((5)F) inserts into O2 by forming several different Ir(+)(O2) complexes. These can then couple along additional surfaces to form low-lying states of the dioxide IrO2(+). The very interesting parallel behavior of the Re, Os, and Ir heavy metal systems is explored in terms of adiabatic and nonadiabatic behavior, although no unambiguous explanation is evident.