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

Reactions of the late third-row transition metal cation Au+ with H2, D2, and HD are examined using guided ion beam tandem mass spectrometry. A flow tube ion source produces Au+ in its 1S (5d10) electronic ground state level. Corresponding state-specific reaction cross sections for forming AuH+ and AuD+ as a function of kinetic energy are obtained and analyzed to give a 0 K bond dissociation energy of D0(Au+?H) = 2.13 ? 0.11 eV. Quantum chemical calculations at the B3LYP/HW+/6- 311+G(3p) and B3LYP/Def2TZVPP levels performed here show good agreement with the experimental bond energy. Theory also provides the electronic structures of these species and the reactive potential energy surfaces. We also compare this third-row transition metal system with previous results for analogous reactions of the first-row and second-row congeners, Cu+ and Ag+. We find that Au+ has a stronger M+?H bond, which can be explained by the lanthanide contraction and relativistic effects that alter the relative size of the valence s and d orbitals. Results from reactions with HD provide insight into the reaction mechanism and indicate that ground state Au+ reacts largely via a direct mechanism, in concordance with the behavior of the lighter group 11 metal ions, but includes more statistical behavior than these metals as well.