REACTIONS OF RU-2, HD, AND D-2(, RH+, PD+, AND AG+ WITH H)

Guided ion beam mass spectrometry has been used to examine the kinetic energy dependence of reactions of the second-row transition-metal cat ions, Ru+, Rh+, Pd+, and Ag+, with molecular hydrogen and its isotopol ogues. By using a meter long flow tube ion source, we are able to crea te Ru+, Rh+, Pd+, and Ag+ ions that are believed to be in their electr onic ground state terms and primarily in the lowest spin-orbit levels. Corresponding state-specific reaction cross sections are obtained. An alysis of the cross section data yields 0 K bond dissociation energies of D-0(Ru+-H) = 1.62 +/- 0.05 eV, D-0(Rh+-H) = 1.67 +/- 0.04 eV, D-0( Pd+-H) = 2.07 +/- 0.04 eV, and D-0(Ag+-H) = 0.41 +/- 0.06 eV. This the rmochemistry is compared with theoretical calculations and previous ex perimental measurements. Periodic trends in these bond dissociation en ergies and the bonding character of these metal hydride ions are discu ssed. Results for the HD reactions indicate that Rh+, Ru+, Pd+, and Ag + ions react via direct mechanisms. The reaction mechanisms and reacti vity differences among these ions are explained using simple molecular orbital concepts.