Potential energy surface for activation of methane by Pt+:: A combined guided ion beam and DFT study

A guided-ion beam tandem mass spectrometer is used to study the reactions of Pt+ with methane, PtCH2+ with H-2 and D-2, and collision-induced dissociation of PtCH4+ and PtCH2+ with Xe. These studies experimentally probe the potential energy surface for the activation of methane by Pt+. For the reaction of Pt+ with methane, dehydrogenation to form PtCH2+ + H-2 is exothermic, efficient, and the only process observed at low energies. PtH+, formed in a simple C-H bond cleavage, dominates the product spectrum at high energies. The observation of a PtH2+ product provides evidence that methane activation proceeds via a (H)(2)PtCH2+ intermediate. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energies in eV (kJ/mol) of D-0(Pt+-H) = 2.81 +/- 0.05 (271 +/- 5), D-0(Pt+-2H) = 6.00 +/- 0.12 (579 +/- 12), D-0(Pt+-C) = 5.43 +/- 0.05 (524 +/- 5), D-0(Pt+-CH) = 5.56 +/- 0.10 (536 +/- 10), and D-0(Pt+-CH3) = 2.67 +/- 0.08 (258 +/- 8). D-0(Pt+-CH2) = 4.80 +/- 0.03 eV (463 +/- 3 kJ/mol) is determined by measuring the forward and reverse reaction rates for Pt+ + CH4 reversible arrow PtCH2+ + H-2 at thermal energy. We find extensive hydrogen scrambling in the reaction of PtCH2+ with D-2 Collision-induced dissociation (CID) of PtCH4+, identified as the H-Pt+-CH3 intermediate, with Xe reveals a bond energy of 1.77 +/- 0.08 eV (171 +/- 8 kJ/mol) relative to Pt+ + CH4 The experimental thermochemistry is favorably compared with density functional theory calculations (B3LYP using several basis sets), which also establish the electronic structures of these species and provide insight into the reaction mechanism. Results for the reaction of Pt+ with methane are compared with those for the analogous palladium system and the differences in reactivity and mechanism are discussed.