CO activation by copper oxide clusters: size, composition, and charge state dependence.

The interaction of CO with copper oxide clusters of different size, composition, and charge is investigated infrared multiple-photon dissociation (IR-MPD) spectroscopy and density functional theory (DFT) calculations. Laser ablation of a copper target in the presence of an O/He mixture leads to the preferred formation of oxygen-rich copper oxide cluster cations, CuO ( > ; ≤ 8), while the anionic cluster distribution is dominated by stoichiometric ( = ) and oxygen-deficient ( < ; ≤ 8) species. Subsequent reaction of the clusters with CO in a flow tube reactor results in the preferred formation of near-stoichiometric CuO(CO) complexes.

Infrared Spectroscopic Characterization of Early 4d Transition Metal Carbene Cations, ZrCH and NbCH.

IR multiple-photon dissociation (IRMPD) action spectroscopy is combined with quantum chemical calculations to examine the [M,C,2H] species for the early 4d metals, M = Zr and Nb. These ions were formed by reacting laser ablated M ions with cyclopropane (-CH) in a molecular beam apparatus. Both IRMPD spectra exhibit one major band near 700 cm and a second weaker band at about twice that wavenumber, more evident when irradiated in focus.

Laboratory infrared spectra and fragmentation chemistry of sulfur allotropes.

Sulfur is one of six life-essential elements, but its path from interstellar clouds to planets and their atmospheres is not well known. Astronomical observations in dense clouds have so far been able to trace only 1 percent of cosmic sulfur, in the form of gas phase molecules and volatile ices, with the missing sulfur expected to be locked in a currently unidentified form. The high sulfur abundances inferred in icy and rocky solar system bodies indicate that an efficient pathway must exist from volatile atomic sulfur in the diffuse interstellar medium to some form of refractory sulfur.

Gas-Phase Production of Hydroxylated Silicon Oxide Cluster Cations: Structure, Infrared Spectroscopy, and Astronomical Relevance.

The interaction of free cationic silicon oxide clusters, Si O ( = 2-5, ≥ ), with dilute water vapor, was investigated in a flow tube reactor. Product mass distributions indicate cluster size-dependent dissociative water adsorption. To probe the structure and vibrational spectra of the resulting Si O H ( = 2-4) clusters, we employed infrared multiple photon dissociation spectroscopy and density functional theory calculations.

Direct probing of low-energy intra d-band transitions in gas-phase cobalt clusters.

The interplay between constituent localized and itinerant electrons of metal clusters defines their physical and chemical properties. In turn, the electronic and geometrical structures are strongly entwined and exhibit strong size-dependent variations. Current understanding of low-energy excited states of metal clusters relies on stand-alone theoretical investigations and few comparisons with measured properties, since direct identification of low-lying states is lacking hitherto.

IR spectroscopic characterization of [M,C,2H] (M = Ru and Rh) products formed by reacting 4d transition metal cations with oxirane: Spectroscopic evidence for multireference character in RhCH.

A combination of infrared multiple-photon dissociation (IRMPD) action spectroscopy and quantum chemical calculations was employed to investigate the [M,C,2H] (M = Ru and Rh) species. These ions were formed by reacting laser ablated M ions with oxirane (ethylene oxide, c-CHO) in a room-temperature ion trap. IRMPD spectra for the Ru species exhibit one major band and two side bands, whereas spectra for the Rh species contain more distinct bands.

IR spectroscopic characterization of 3d transition metal carbene cations, FeCH and CoCH: periodic trends and a challenge for DFT approaches.

A combination of IR multiple-photon dissociation (IRMPD) action spectroscopy and quantum chemical calculations was employed to investigate the [M,C,2H] (M = Fe and Co) species. These were formed by reacting laser ablated M ions with oxirane (ethylene oxide, c-CHO) in a room temperature ion trap. IRMPD spectra for the Fe and Co species are very similar and exhibit one major band.

Characterization of CO Adsorbed to Clean and Partially Oxidized Cu(211) and Cu(111).

Copper-based catalysts gain activity through the presence of poorly coordinated Cu atoms and incomplete oxidation at the surface. The catalytic mechanisms can in principle be observed by controlled dosing of reactants to single-crystal substrates. However, the interconnected influences of surface defects, partial oxidation, and adsorbate coverage present a large matrix of conditions that have not been fully explored in the literature.

Cluster size dependent coordination of formate to free manganese oxide clusters.

The interaction of free manganese oxide clusters, MnO ( = 1-9, = 0-12), with formic acid was studied infrared multiple-photon dissociation (IR-MPD) spectroscopy together with calculations using density functional theory (DFT). Clusters containing only one Mn atom, such as MnO and MnO, bind formic acid as an intact molecule in both the - and -configuration. In contrast, all clusters containing two or more manganese atoms deprotonate the acid's hydroxyl group.

Pentagon, Hexagon, or Bridge? Identifying the Location of a Single Vanadium Cation on Buckminsterfullerene Surface.

Buckminsterfullerene C has received extensive research interest since its discovery. In addition to its interesting intrinsic properties of exceptional stability and electron-accepting ability, the broad chemical tunability by decoration or substitution on the C-fullerene surface makes it a fascinating molecule. However, to date, there is uncertainty about the binding location of such decorations on the C surface, even for a single adsorbed metal atom.

Carbon Dioxide and Water Activation by Niobium Trioxide Anions in the Gas Phase.

Transition metals are important in various industrial applications including catalysis. Due to the current concentration of CO in the atmosphere, various ways for its capture and utilization are investigated. Here, we study the activation of CO and HO at [NbO] in the gas phase using a combination of infrared multiple photon dissociation spectroscopy and density functional theory calculations.

Spectroscopic evidence of a Xe-Xe bond in the linear XeAuXe ion.

The closed-shell nature of Xe atoms precludes the formation of Xe-Xe bonds other than based on van der Waals interactions. Here, we present experimental evidence showing that the complexation of Xe atoms to a Au ion leads to stabilization of a Xe-Xe interaction going beyond purely dispersive. Infrared spectroscopy is used to identify the geometry of AuXe as a linear structure in which two Xe atoms form a direct bond, instead of an expected geometry in which three Xe atoms coordinate directly with a central Au ion.

Tuning the degree of CO activation by carbon doping Cu ( = 3-10) clusters: an IR spectroscopic study.

Copper clusters on carbide surfaces have shown a high catalytic activity towards methanol formation. To understand the interaction between CO and the catalytically active sites during this process and the role that carbon atoms could play in this, they are modeled by copper clusters, with carbon atoms incorporated. The formed clusters CuC ( = 3-10, = 1-2) are reacted with CO and investigated by IR multiple-photon dissociation (IR-MPD) spectroscopy to probe the degree of CO activation.

NO Bond Cleavage on Gas-Phase Ir Clusters Investigated by Infrared Multiple Photon Dissociation Spectroscopy.

The adsorption forms of NO on Ir ( = 3-6) clusters were investigated using infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations. Spectral features indicative both for molecular NO adsorption (the NO stretching vibration in the 1800-1900 cm range) and for dissociative NO adsorption (the terminal Ir-O vibration around 940 cm) were observed, elucidating the co-existence of molecular and dissociative adsorption of NO. In all calculated structures for molecular adsorption, NO is adsorbed via the N atom on on-top sites.

RAIRS Characterization of CO and O Coadsorption on Cu(111).

In a study preliminary to investigating CO dissociation, we report our results on oxygen and carbon monoxide coadsorption on Cu(111). We use reflection adsorption infrared spectroscopy and Auger electron spectroscopy to characterize and quantify adsorbed species. On clean Cu(111), the CO internal stretch mode appears initially at 2077 cm for a surface temperature of ∼80 K.

C-H Bond Activation and C-C Coupling of Methane on a Single Cationic Platinum Center: A Spectroscopic and Theoretical Study.

We spectroscopically investigated the activation products resulting from reacting one and multiple methane molecules with Pt ions. Pt ions were formed by laser ablation of a metal target and were cooled to the electronic ground state in a supersonic expansion. The ions were then transferred to a room temperature ion trap, where they were reacted with methane at various partial pressures in an argon buffer gas.

Bonding Nature between Noble Gases and Small Gold Clusters.

Noble gases are usually seen as utterly inert, likewise gold, which is typically conceived as the noblest of all metals. While one may expect that noble gases bind to gold via dispersion interactions only, strong bonds can be formed between noble gas atoms and small gold clusters. We combine mass spectrometry, infrared spectroscopy, and density functional theory calculations to address the bonding nature between Au ( ≤ 4) clusters and Ar, Kr, and Xe.

IR Spectroscopic Characterization of Methane Adsorption on Copper Clusters Cu ( = 2-4).

The interaction of CH with cationic copper clusters has been studied with infrared-multiple photon dissociation (IRMPD) spectroscopy. Cu ( = 2-4) formed by laser ablation were reacted with CH. The formed complexes were irradiated with the IR light of the free-electron laser for intracavity experiments (FELICE), and the fragments were mass-analyzed with a reflectron time-of-flight mass spectrometer.

Zooming in on the initial steps of catalytic NO reduction using metal clusters.

The study of reactions relevant to heterogeneous catalysis on the surface of well-defined metal clusters with full control over the number of consituent atoms and elemental composition can lead to a detailed insight into the interactions between metal and reactants. We here review experimental and theoretical studies involving the adsorption of NO molecules on mostly rhodium-based clusters under near-thermal conditions in a molecular beam. We show how IR spectrosopic characterization can give information on the binding nature of NO to the clusters for at least the first three NO molecules.

Adsorption Forms of NO on Iridium-Doped Rhodium Clusters in the Gas Phase Revealed by Infrared Multiple Photon Dissociation Spectroscopy.

The adsorption of an NO molecule on a cationic iridium-doped rhodium cluster, RhIr, was investigated by infrared multiple photon dissociation spectroscopy (IRMPD) of RhIrNO·Ar complexes in the 300-2000 cm spectral range, where the Ar atoms acted as a messenger signaling IR absorption. Complementary density functional theory (DFT) calculations predicted two near-isoenergetic structures as the putative global minimum: one with NO adsorbed in molecular form in the on-top configuration on the Ir atom in RhIr, and one where NO is dissociated with the O atom bound to the Ir atom in the on-top configuration and the N atom on a hollow site formed by three Rh atoms. A comparison between the experimental IRMPD spectrum of RhIrNO and calculated spectra indicated that NO mainly adsorbs molecularly on RhIr, but evidence was also found for structures with dissociatively adsorbed NO.

The size-dependent influence of palladium doping on the structures of cationic gold clusters.

The physicochemical properties of small metal clusters strongly depend on their precise geometry. Determining such geometries, however, is challenging, particularly for clusters formed by multiple elements. In this work, we combine infrared multiple photon dissociation spectroscopy and density functional theory calculations to investigate the lowest-energy structures of Pd doped gold clusters, PdAu ( ≤ 10).

IR spectroscopic characterization of the co-adsorption of CO and H onto cationic Cu clusters.

To understand elementary reaction steps in the hydrogenation of CO over copper-based catalysts, we experimentally study the adsorption of CO and H onto cationic Cu clusters. For this, we react Cu clusters formed by laser ablation with a mixture of H and CO in a flow tube-type reaction channel and characterize the products formed by IR multiple-photon dissociation spectroscopy employing the IR free-electron laser FELICE. We analyze the spectra by comparing them to literature spectra of Cu clusters reacted with H and with new spectra of Cu clusters reacted with CO.