Gold Clusters in the Gas Phase

Gold clusters exhibit strong size and charge state dependent variations in their properties. This is demonstrated by significant changes in their geometric structures and also in their chemical properties. Here we focus on clusters containing up to about 20 gold atoms and briefly review their structural evolution emphasising the role of isomerism and structural fluxionality. The discussion of chemical properties is limited to the interaction of gold clusters with molecular oxygen and carbon monoxide, separately, and their interaction in CO/O2 co-adsorbates on gold clusters eventually leading to CO oxidation. Whilst highlighting results obtained using different experimental approaches, special attention is given to the insights obtained using infrared multiple photon dissociation (IR-MPD) spectroscop

CO adsorption on neutral iridium clusters

The adsorption of carbon monoxide on neutral iridium clusters in the size range of n = 3 to 21 atoms is investigated with infrared multiple photon dissociation spectroscopy. For each cluster size only a single v(CO) band is present with frequencies in the range between 1962 cm-1 (n = 8) and 1985 cm-1 (n = 18) which can be attributed to an atop binding geometry. This behaviour is compared to the CO binding geometries on clusters of other group 9 and 10 transition metals as well as to that on extended surfaces. The preference of Ir for atop binding is rationalized by relativistic effects on the electronic structure of the later 5d metals

Imaging Photoelectron Circular Dichroism in the Detachment of Mass‐Selected Chiral Anions

Photoelectron Circular Dichroism (PECD) is a forward-backward asymmetry in the photoemission from a non-racemic sample induced by circularly polarized light. PECD spectroscopy has potential analytical advantages for chiral discrimination over other chiroptical methods due to its increased sensitivity to the chiral potential of the molecule. The use of anions for PECD spectroscopy allows for mass-selectivity and provides a path to simple experimental schemes that employ table-top light sources. Evidence of PECD for anions is limited, and insight into the forces that govern PECD electron dynamics in photodetachment is absent. Here, we demonstrate a PECD effect in the photodetachment of mass-selected deprotonated 1-indanol anions. By utilizing velocity map imaging photoelectron spectroscopy with a tunable light source, we determine the energy-resolved PECD over a wide range of photon energies. The observed PECD reaches up to 11%, similar to what has been measured for neutral species

Atomic Cluster Au₁₀⁺ Is a Strong Broadband Midinfrared Chromophore

We report an intense broadband midinfrared absorption band in the Au10+ cluster in a region in which only molecular vibrations would normally be expected. Observed in the infrared multiple photon dissociation spectra of Au10Ar+, Au10(N2O)+, and Au10(OCS)+, the smooth feature stretches 700–3400  cm-1 (λ=14–2.9  μm). Calculations confirm unusually low-energy allowed electronic excitations consistent with the observed spectra. In Au10(OCS)+, IR absorption throughout the band drives OCS decomposition resulting in CO loss, providing an alternative method of bond activation or breaking

Aufklärung der Struktur von Metallclustern durch Schwingungsspektroskopie

Application of a new method of infrared spectroscopy delivers insights into the atomic structure of clusters composed of only a few metal atoms

Comparison of Conventional and Nonconventional Hydrogen Bond Donors in Au^- Complexes

Although gold has become a well-known nonconventional hydrogen bond acceptor, interactions with nonconventional hydrogen bond donors have been largely overlooked. In order to provide a better understanding of these interactions, two conventional hydrogen bonding molecules (3-hydroxytetrahydrofuran and alaninol) and two nonconventional hydrogen bonding molecules (fenchone and menthone) were selected to form gas-phase complexes with Au-. The Au-[M] complexes were investigated using anion photoelectron spectroscopy and density functional theory. Au-[fenchone], Au-[menthone], Au-[3-hydroxyTHF], and Au-[alaninol] were found to have vertical detachment energies of 2.71 ± 0.05, 2.76 ± 0.05, 3.01 ± 0.03, and 3.02 ± 0.03 eV, respectively, which agree well with theory. The photoelectron spectra of the complexes resemble the spectrum of Au- but are blueshifted due to the electron transfer from Au- to M. With density functional theory, natural bond orbital analysis, and atoms-in-molecules analysis, we were able to extend our comparison of conventional and nonconventional hydrogen bonding to include geometric and electronic similarities. In Au-[3-hydroxyTHF] and Au-[alaninol], the hydrogen bonding comprised of Au-···HO as a strong, primary hydrogen bond, with secondary stabilization by weaker Au-···HN or Au-···HC hydrogen bonds. Interestingly, the Au-···HC bonds in Au-[fenchone] and Au-[menthone] can be characterized as hydrogen bonds, despite their classification as nonconventional hydrogen bond donors

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

Vibrational spectra and structures of bare and Xe-tagged cationic Si_nO_m⁺ clusters

Vibrational spectra of Xe-tagged cationic silicon oxide clusters SinOm+ with n = 3–5 and m = n, n ± 1 in the gas phase are obtained by resonant infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations. The SinOm+ clusters are produced in a laser vaporization ion source and Xe complexes are formed after thermalization to 100 K. The clusters are subsequently irradiated with tunable light from an IR free electron laser and changes in the mass distribution yield size-specific IR spectra. The measured IRMPD spectra are compared to calculated linear IR absorption spectra leading to structural assignments. For several clusters, Xe complexation alters the energetic order of the SinOm+ isomers. Common structural motifs include the Si2O2 rhombus, the Si3O2 pentagon, and the Si3O3 hexagon

Disparate Effects of Cu and V on Structures of Exohedral Transition Metal-Doped Silicon Clusters: A Combined Far-Infrared Spectroscopic and Computational Study

The growth mechanisms of small cationic silicon clusters containing up to 11 Si atoms, exohedrally doped by V and Cu atoms, are described. We find that as dopants, V and Cu follow two different paths: while V prefers substitution of a silicon atom in a highly coordinated position of the cationic bare silicon clusters, Cu favors adsorption to the neutral or cationic bare clusters in a lower coordination site. The different behavior of the two transition metals becomes evident in the structures of SinM+ (n = 4−11 for M = V, and n = 6−11 for M = Cu), which are investigated by density functional theory and, for several sizes, confirmed by comparison with their experimental vibrational spectra. The spectra are measured on the corresponding SinM+·Ar complexes, which can be formed for the exohedrally doped silicon clusters. The comparison between experimental and calculated spectra indicates that the BP86 functional is suitable to predict far-infrared spectra of these clusters. In most cases, the calculated infrared spectrum of the lowest-lying isomer fits well with the experiment, even when various isomers and different electronic states are close in energy. However, in a few cases, namely Si9Cu+, Si11Cu+, and Si10V+, the experimentally verified isomers are not the lowest in energy according to the density functional theory calculations, but their structures still follow the described growth mechanism. The different growth patterns of the two series of doped Si clusters reflect the role of the transition metal’s 3d orbitals in the binding of the dopant atoms