Argon tagging of doubly transition metal doped aluminum clusters: The importance of electronic shielding

The interaction of argon with doubly transition metal doped aluminum clusters, AlnTM2+ (n = 1–18, TM = V, Nb, Co, Rh), is studied experimentally in the gas phase via mass spectrometry. Density functional theory calculations on selected sizes are used to understand the argon affinity of the clusters, which differ depending on the transition metal dopant. The analysis is focused on two pairs of consecutive sizes: Al6,7V2+ and Al4,5Rh2+, the largest of each pair showing a low affinity toward Ar. Another remarkable observation is a pronounced drop in reactivity at n = 14, independent of the dopant element. Analysis of the cluster orbitals shows that this feature is not a consequence of cage formation but is electronic in nature. The mass spectra demonstrate a high similarity between the size-dependent reactivity of the clusters with Ar and H2. Orbital interactions provide an intuitive link between the two and further establish the importance of precursor states in the reactions of the clusters with hydrogen

An octacoordinated Nb atom in the NbAl₈H₈⁺ cluster

The NbAl8H8+ cluster was formed in a molecular beam and characterized by mass spectrometry and infrared spectroscopy. Density functional theory calculations show the lowest-energy isomer is a high symmetry singlet with the Nb atom placed at the center of a distorted hexagonal Al ring and coordinated by two AlH moieties, therefore exhibiting octacoordination. The unprecedented high-symmetric geometry is attributed to the 20 valence electrons; the central Nb atom adheres to the 18-electron rule and two additional delocalized electrons stabilize the hexagonal ring

Hydrogen Chemisorption on Doubly Vanadium Doped Aluminum Clusters

Producción CientíficaThe interaction of hydrogen with doubly vanadium doped aluminum clusters, AlnV2+ (n = 1–12), is studied experimentally by time-of-flight mass spectrometry and infrared multiple photon dissociation spectroscopy. The hydrogen binding geometry is inferred from comparison with infrared spectra predicted by density functional theory and shows that for the more reactive clusters the hydrogen adsorbs dissociatively. Three sizes, n = 4, 5 and 7, are remarkably unreactive compared to the other clusters. For larger sizes the reactivity decreases, a behavior that is similar to that of singly vanadium doped aluminum clusters, and that might be attributed to geometric and/or electronic shielding of the dopants. By examining the electronic structure of Al6V2+ and Al7V2+, interactions between the frontier orbitals of the clusters and those of H2 that explain the size-dependent reactivity are identified.Ministerio de Economía, Industria y Competitividad (Project RYC-2014-15261

Effects of Charge Transfer on the Adsorption of CO on Small Molybdenum-Doped Platinum Clusters

The interaction of carbon monoxide with platinum alloy nanoparticles is an important problem in the context of fuel cell catalysis. In this work, molybdenum-doped platinum clusters have been studied in the gas phase to obtain a better understanding of the fundamental nature of the Pt–CO interaction in the presence of a dopant atom. For this purpose, Ptn+ and MoPtn-1+ (n=3–7) clusters were studied by combined mass spectrometry and density functional theory calculations, making it possible to investigate the effects of molybdenum doping on the reactivity of platinum clusters with CO. In addition, IR photodissociation spectroscopy was used to measure the stretching frequency of CO molecules adsorbed on Ptn+ and MoPtn-1+ (n=3–14), allowing an investigation of dopant-induced charge redistribution within the clusters. This electronic charge transfer is correlated with the observed changes in reactivity

Towards a learning organisation

As we face a revolutionary move towards e-learning and away from traditional face-to-face training, today's human resource manager implementing technology-supported training needs a concise, practical handbook outlining the choices that have to be made and the implications of each approach. 'Towards a learning organisation' brings human resource managers up-to-date with the various applications that are open to them, such as Electronic Learning Environments, Web based training, Videoconferencing, etc. This handbook provides user-friendly information about emerging technologies for training, checklists and other decision-making tools. Based on broad experience and peppered throughout with case studies and examples from leading European companies and institutions, it also offers plenty of background information including an onverview of network options as well as a handy glossary and further resources list

Hydrogen Adsorption and Dissociation on Al_nRh₂⁺ (n=1 to 9) Clusters: Steric and Coordination Effects

The interaction of molecular hydrogen with doubly rhodium doped aluminum clusters, AlnRh2+ (n = 1 to 9), is investigated by a combination of time-of-flight mass spectrometry, infrared multiple photon dissociation spectroscopy, and density functional theory calculations. The reactivity of the AlnRh2+ clusters toward H2 is found to be sensitive to cluster size, with sizes n = 1 to 4 and 7 being the most reactive. Al3Rh2+ and Al4Rh2+ are the only species that thermodynamically prefer molecular over dissociative H2 adsorption. Calculated molecular adsorption energies of a single H2 molecule correlate well with the experimental abundances of the hydrogenated species, and the potential energy profiles reveal that H2 dissociation only has submerged barriers for n = 1, 2, and 7. In contrast, the molecularly hydrogenated complexes seem to be kinetically trapped for n = 5, 6, 8, and 9 due to significant energy barriers. This indicates that the initial molecular H2 adsorption on the Rh atoms and thereafter dissociation are the determining steps for the hydrogenation reaction. An analysis of the cluster geometries reveals that the coordination environment and the steric factor of the Rh atoms are the main descriptors for the size-dependent reactivity of the AlnRh2+ clusters

The redox environment differentially regulates autophagy in leaves and roots of Arabidopsis thaliana during cadmium stress

Resumen del poster presentado en: Redox Biology Congress. Gante, Bélgica; 24-26 de agosto (2022

Competitive Molecular and Dissociative Hydrogen Chemisorption on Size Selected Doubly Rhodium Doped Aluminum Clusters

The interaction of hydrogen with AlnRh2+ (n = 10–13) clusters is studied by mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. Comparing the IRMPD spectra with predictions obtained using density functional theory calculations allows for the identification of the hydrogen binding geometry. For n = 10 and 11, a single H2 molecule binds dissociatively, whereas for n = 12 and 13, it adsorbs molecularly. Upon adsorption of a second H2 to Al12Rh2+, both hydrogen molecules dissociate. Theoretical calculations suggest that the molecular adsorption for n = 12 and 13 is not due to kinetic impediment of the hydrogenation reaction by an activation barrier, but due to a higher binding energy of the molecularly adsorbed hydrogen–cluster complex. Inspection of the highest occupied molecular orbitals shows that the hydrogen molecule initially forms a strongly bound Kubas complex with the Al11-13Rh2+ clusters, whereas it only binds weakly with Al10Rh2+

Size Dependent H₂ Adsorption on Al_nRh⁺ (n = 1–12) Clusters

The interaction of hydrogen with singly rhodium doped aluminum clusters AlnRh+ (n = 1–12) is investigated experimentally by a combination of time-of-flight mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. Density functional theory (DFT) is employed to optimize the geometric and electronic structures of bare and hydrogenated AlnRh+ clusters and the obtained infrared spectra of hydrogenated clusters are compared with the corresponding IRMPD spectra. The reactivity of the AlnRh+ clusters toward H2 is found to be strongly size-dependent, with n = 1–3, and 7 being the most reactive. Furthermore, it is favorable for H2 to adsorb molecularly on Al2Rh+ and Al3Rh+, while it prefers dissociative adsorption on other sizes. The initial molecular adsorption of H2 is identified as the determining step for hydrogen interaction with the AlnRh+ clusters, because the calculated molecular adsorption energies of H2 correlate well with the experimental abundances of the hydrogenated clusters. Natural charge populations and properties of the AlnRh+ clusters are analyzed to interpret the observed size-dependent reactivity

Water Splitting by C60-Supported Vanadium Single Atoms

Contains fulltext : 244891.pdf (Publisher’s version ) (Closed access