Guided ion beam and theoretical study of the reactions of Os+ with H2, D2, and HD

Reactions of the third-row transition metal cation Os+ with H-2, D-2, and HD to form OsH+ (OsD+) were studied using a guided ion beam tandem mass spectrometer. A flow tube ion source produces Os+ in its D-6 (6s(1)5d(6)) electronic ground state level. Corresponding state-specific reaction cross sections are obtained. The kinetic energy dependences of the cross sections for the endothermic formation of OsH+ and OsD+ are analyzed to give a 0 K bond dissociation energy of D-0(Os+-H) = 2.45 +/- 0.10 eV. Quantum chemical calculations are performed here at several levels of theory, with B3LYP approaches generally overestimating the experimental bond energy whereas results obtained using BHLYP and CCSD(T), coupled-cluster with single, double, and perturbative triple excitations, levels show good agreement. Theory also provides the electronic structures of these species and the potential energy surfaces for reaction. Results from the reactions with HD provide insight into the reaction mechanism and indicate that Os+ reacts via a direct reaction. We also compare this third-row transition metal system with the first-row and second-row congeners, Fe+ and Ru+, and find that Os+ reacts more efficiently with dihydrogen, forming a stronger M+-H bond. These differences can be attributed to the lanthanide contraction and relativistic effects. (C) 2011 American Institute of Physics. [doi:10.1063/1.3669425]