Abstract
A combined spectroscopic and computational study of gas-phase Au+(CH4)n (n = 3–8) complexes reveals a strongly-bound linear Au+(CH4)2 core structure to which up to four additional ligands bind in a secondary coordination shell. Infrared resonance-enhanced photodissociation spectroscopy in the region of the CH4a1 and t2 fundamental transitions reveals essentially free internal rotation of the core ligands about the H4C–Au+–CH4 axis, with sharp spectral features assigned by comparison with spectral simulations based on density functional theory. In separate experiments, vibrationally-enhanced dehydrogenation is observed when the t2 vibrational normal mode in methane is excited prior to complexation. Clear infrared-induced enhancement is observed in the mass spectrum for peaks corresponding 4u below the mass of the Au+(CH4)n=2,3 complexes corresponding, presumably, to the loss of two H2 molecules.
Highlights
Isolated gas-phase metal ion–ligand clusters in many ways represent ideal model systems for studying fundamental metal–ligand interactions
Many industrial heterogeneous catalysts typically comprise multiple components, with reactions assumed to occur at metal defects supported by a macroscopic bulk structure [1]
The model systems studied can capture some of the features and energetics of the surface of catalysts [2], without complications arising from the bulk structure
Summary
Isolated gas-phase metal ion–ligand clusters in many ways represent ideal model systems for studying fundamental metal–ligand interactions. The ultimate goal is to better understand the fundamental interactions and mechanisms underlying the key catalytic processes in order to develop cost-efficient strategies for methane (and other hydrocarbons) activation To this end, a wide variety of fundamental experimental and theoretical studies have investigated the reactivity of bare transition metal monocations with methane [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56]. We have observed enhanced dehydrogenation when methane is vibrationally excited prior to interaction with Au+
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