13 research outputs found
Pentagon, Hexagon, or Bridge? Identifying the Location of a Single Vanadium Cation on Buckminsterfullerene Surface
Buckminsterfullerene C60 has received extensive research interest ever 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 C60-fullerene surface makes it
a fascinating molecule. However, to date there is uncertainty about the binding
location of such decorations on the C60 surface, even for a single adsorbed
metal atom. In this work, we report the gas-phase synthesis of the C60V+
complex and its in-situ characterization by mass spectrometry and in-frared
spectroscopy with the help of quantum chemical calculations and molecular
dynamics simulations. We identify the most probable binding position of a
vanadium cation on C60 above a pentagon center in eta5-fashion, demonstrate a
high thermal stability for this complex, and explore the bonding nature between
C60 and the vanadium cation, reveal-ing that large orbital and electrostatic
interactions lie at the origin of the stability of the eta5-C60V+ complex.Comment: 29 pages (11 pages for main text and 17 pages for the supporting
information
Not Completely Innocent:How Argon Binding Perturbs Cationic Copper Clusters
Contains fulltext :
226671.pdf (publisher's version ) (Open Access)7 p
Tuning the degree of CO2 activation by carbon doping Cun- (n = 3â10) clusters: an IR spectroscopic study
Copper clusters on carbide surfaces have shown a high catalytic activity towards methanol
formation. To understand the interaction between CO2 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 CunCm- (n=3â10, m = 1â2) are reacted with CO2 and investigated by IR multiple-photon
dissociation (IR-MPD) spectroscopy to probe the degree of CO2 activation. IR spectra for the reaction products [CunCCO2]-, (n = 6â10), and [CunC2.CO2]-, (n = 3â8) are
compared to reference spectra recorded for products formed when reacting the same cluster sizes with CO, and with density functional theory (DFT) calculated spectra. The
results reveal a size- and carbon load-dependent activation and dissociation of CO2. The complexes [CunC.CO2]- with n = 6 and 10 show predominantly molecular activation of CO2, while those with n = 7â9 show only dissociative adsorption. The addition of the second carbon to the cluster leads to the exclusive molecular activation of the CO2 on all measured cluster sizes, except for Cu5C2- where CO2 dissociates. Combining these ïŹndings with DFT calculations leads us to speculate that at lower carbon-to-metal ratios (CMRs), the C can act as an oxygen anchor facilitating the OC=O bond rupture, whereas at higher CMRs the carbon atoms increasingly attract negative charge, reducing the Cu clusterâs ability to donate electron density to CO2, and
consequently its ability to activate CO2
Efficient Formation of Size-Selected Clusters upon Pickup of Dopants into Multiply Charged Helium Droplets
Properties of clusters often depend critically on the exact number of atomic or molecular building blocks, however, most methods of cluster formation lead to a broad, size distribution and cluster intensity anomalies that are often designated as magic numbers. Here we present a novel approach of breeding size-selected clusters via pickup of dopants into multiply charged helium nanodroplets. The size and charge state of the initially undoped droplets and the vapor pressure of the dopant in the pickup region, determines the size of the dopant cluster ions that are extracted from the host droplets, via evaporation of the helium matrix in a collision cell filled with room temperature helium or via surface collisions. Size distributions of the selected dopant cluster ions are determined utilizing a high-resolution time of flight mass spectrometer. The comparison of the experimental data, with simulations taking into consideration the pickup probability into a shrinking He droplet due to evaporation during the pickup process, provides a simple explanation for the emergence of size distributions that are narrower than Poisson
Efficient Formation of Size-Selected Clusters upon Pickup of Dopants into Multiply Charged Helium Droplets
Properties of clusters often depend critically on the exact number of atomic or molecular building blocks, however, most methods of cluster formation lead to a broad, size distribution and cluster intensity anomalies that are often designated as magic numbers. Here we present a novel approach of breeding size-selected clusters via pickup of dopants into multiply charged helium nanodroplets. The size and charge state of the initially undoped droplets and the vapor pressure of the dopant in the pickup region, determines the size of the dopant cluster ions that are extracted from the host droplets, via evaporation of the helium matrix in a collision cell filled with room temperature helium or via surface collisions. Size distributions of the selected dopant cluster ions are determined utilizing a high-resolution time of flight mass spectrometer. The comparison of the experimental data, with simulations taking into consideration the pickup probability into a shrinking He droplet due to evaporation during the pickup process, provides a simple explanation for the emergence of size distributions that are narrower than Poisson
The structures of cationic gold clusters probed by far-infrared spectroscopy
Determining the precise structures of small gold clusters is an essential step towards understanding their chemical and physical properties. Due to the relativistic nature of gold, its clusters remain planar (2D) up to appreciable sizes. Ion mobility experiments have suggested that positively charged gold clusters adopt three-dimensional (3D) structures from n = 8 onward. Computations predict, depending on the level of theory, 2D or 3D structures as putative energy-minimum for n = 8. In this work, far-infrared multiple photon dissociation spectroscopy, using Ar as tagging element, is combined with density-functional theory calculations to determine the structures of Aun+ (n†9) clusters formed by laser ablation. While the Au frameworks in Au6Arm+ and Au7Arm+ complexes are confirmed to be planar and that in Au9Arm+ three-dimensional, we demonstrate the coexistence of 3D and planar Au8Arm+ (m = 1-3) isomers. Thus, it is revealed that at finite temperatures, the formal 2D to 3D transition takes place at n = 8 but is not sharp.status: publishe
The structures of cationic gold clusters probed by far-infrared spectroscopy
International audienc
Tuning the Dissociative Action of Cationic Rh Clusters Toward NO by Substituting a Single Ta Atom
Modification
of Rh chemical activity for decomposition of NO by
alloying with Ta was studied by vibrational spectroscopy of gas-phase
clusters, where one single Rh atom was substituted by Ta, with NO
adsorbed. While NO adsorbs molecularly on pure Rh clusters, it was
found to adsorb dissociatively on Rh<sub><i>n</i></sub>Ta<sup>+</sup> (<i>n</i> = 2â8) with the O bound to the
Ta on-top site. A reaction path for NO decomposition obtained by density
functional theory calculations for octahedral Rh<sub>5</sub>Ta<sup>+</sup> and Rh<sub>6</sub><sup>+</sup> suggests that the Ta oxygen
affinity strongly reduces the energy barrier right before bond cleavage,
facilitating NO dissociation. The trend is consistent with the BellâEvansâPolanyi
principle. The addition of other less oxophilic dopant atoms could
plausibly enhance catalytic reactivity of Rh
Structural characterization of [M,C,2H](+) products formed by reaction of 5d metal cations Pt+ and Ir+ with ethylene oxide and Ta+ with methane using messenger spectroscopy
Structural characterization of gas-phase [M,C,2H]+(M = Ta, Ir, Pt), formed by reacting laser ablationformed M+with ethylene oxide (c-C2H4O) or methane under multiple collision conditions, is achievedusing infrared multiple-photon dissociation (IR-MPD) spectroscopy with the intracavity free-electronlaser FELICE. After product formation, part of the product distribution is complexed with Ar, allowingfor simultaneous recording of IR-MPD spectra of both bare [M,C,2H]+, which dissociates viadehydrogenation, and [M,C,2H]+âAr, which loses Ar. Comparison of the spectra with density functionaltheory (DFT) calculations allows for an internally consistent assignment of the spectra to the Ta+CH2(3A00) distorted carbene, Pt+CH2(2A1) carbene, and to the HIr+CH (1A0) carbyne-hydride. Evidence for asymmetric Ta+CH2âAr (3B2) complex is also obtained. For Pt and Ir, these structures match those foundin previous work when these species were formed by reaction of M+with methane, CH4and CD4.Under the current conditions, no clear signs of the previously observed Ir+CH2(3A2) carbene product werefound, consistent with its higher energy, especially after Ar complexation. Potential energy surfaces forthe reactions of Pt+and Ir+with c-C2H4O are also computed
Structures of Cu-n(+) (n=3-10) Clusters Obtained by Infrared Action Spectroscopy
Contains fulltext :
203937.pdf (publisher's version ) (Open Access