A previous infrared multiple photon dissociation (IRMPD) action spectroscopy and density functional theory (DFT) study explored the structures of the [M,C,2H] products formed by dehydrogenation of methane by four, gas-phase 5d transition metal cations (M = Ta, W, Ir, and Pt). Complicating the analysis of these spectra for Ir and Pt was observation of an extra band in both spectra, not readily identified as a fundamental vibration. In an attempt to validate the assignment of these additional peaks, the present work examines the gas phase [M,C,2D] products of the same four metal ions formed by reaction with perdeuterated methane (CD). As before, metal cations are formed in a laser ablation source and react with methane pulsed into a reaction channel downstream, and the resulting products are spectroscopically characterized through photofragmentation using the free-electron laser for intracavity experiments in the 350-1800 cm range. Photofragmentation was monitored by the loss of D for [Ta,C,2D] and [W,C,2D] and of D in the case of [Pt,C,2D] and [Ir,C,2D]. Comparison of the experimental spectra and DFT calculated spectra leads to structural assignments for all [M,C,2H/2D] systems that are consistent with previous identifications and allows a full description of the systematic spectroscopic shifts observed for deuterium labeling of these complexes, some of the smallest systems to be studied using IRMPD action spectroscopy. Further, full rotational contours are simulated for each vibrational band and explain several observations in the present spectra, such as doublet structures in several bands as well as the observed linewidths. The prominent extra bands in the [Pt,C,2D/2H] spectra appear to be most consistent with an overtone of the out-of-plane bending vibration of the metal carbene cation structure.
Methane represents the major constituent of natural gas. It is primarily used only as a source of energy by means of combustion, but could also serve as an abundant hydrocarbon feedstock for high quality chemicals. One of the major challenges in catalysis research nowadays is therefore the development of materials that selectively cleave one of the four C-H bonds of methane and thus make it amenable for further chemical conversion into valuable compounds. By employing infrared spectroscopy and first-principles calculations it is uncovered herein that the interaction of methane with small gold cluster cations leads to selective C-H bond dissociation and the formation of hydrido methyl complexes, H-Au -CH . The distinctive selectivity offered by these gold clusters originates from a fine interplay between the closed-shell nature of the d states and relativistic effects in gold. Such fine balance in fundamental interactions could prove to be a tunable feature in the rational design of a catalyst.
The structures of small cationic silver clusters Ag (n = 3-13) are investigated by comparing measured far-infrared multiple photon dissociation spectra of cluster-argon complexes with the calculated harmonic vibrational spectra of different low-energy structural isomers. A global structure search was carried out using the CALYPSO structure prediction method, after which isomers were locally optimized with the meta GGA functional TPSS. The obtained structures of the cationic silver clusters are mostly consistent with earlier ion mobility measurements and photodissociation spectroscopy studies for Ag (n = 3-11) and allowed excluding several structural isomers that were considered in those earlier studies, which illustrates the strength of combining multiple experimental techniques for conclusive structural identification. The growth pattern of the cationic silver clusters is discussed and differences with other cationic coinage metal clusters are highlighted.
Methane represents the major constituent of natural gas. It is primarily used only as a source of energy by means of combustion, but could also serve as an abundant hydrocarbon feedstock for high quality chemicals. One of the major challenges in catalysis research nowadays is therefore the development of materials that selectively cleave one of the four C−H bonds of methane and thus make it amenable for further chemical conversion into valuable compounds. By employing infrared spectroscopy and first‐principles calculations it is uncovered herein that the interaction of methane with small gold cluster cations leads to selective C−H bond dissociation and the formation of hydrido methyl complexes, H‐Aux+‐CH3. The distinctive selectivity offered by these gold clusters originates from a fine interplay between the closed‐shell nature of the d states and relativistic effects in gold. Such fine balance in fundamental interactions could prove to be a tunable feature in the rational design of a catalyst.
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