Activation of CH4by gas-phase Ni+and the thermochemistry of Ni–ligand complexes

Abstract

The kinetic energy dependence of the reaction of Ni⁺ (²D) with methane has been studied using guided ion beam mass spectrometry. Formation of NiH⁺, NiCH₂ ⁺ and NiCH₃ ⁺ are all observed with thresholds near 2 eV, and NiCH⁺ is observed at higher kinetic energies. The dehydrogenation reaction is shown to proceed over a barrier in excess of the endothermicity by examining the reverse reaction of NiCH₂ ⁺ + D₂. Collision-induced dissociation of NiCH₂ ⁺ and NiCH₄ ⁺ with Xe provides additional information on the products and reaction intermediates. Modeling of the endothermic reaction cross sections yields the 0 K bond dissociation energies (in eV) of D₀(Ni⁺–H) = 1.60 ± 0.08, D₀(Ni⁺–CH) = 3.12 ± 0.12, D₀(Ni⁺–CH₂) = 3.20 ± 0.08, D₀(Ni⁺–CH₃) = 1.76 ± 0.07, and D₀(Ni⁺–CH₄) = 1.00 ± 0.05. The experimental thermochemistry is favorably compared with previous experimental results and density functional theory calculations (B3LYP), which also establish the electronic structures of these species and provide insight into the reaction mechanism. The results for Ni⁺ are compared with those for the third-row transition metal congener Pt⁺ and the differences in behavior and mechanism are discussed.