Trapped Ion Electron Diffraction Research Articles

Determination of geometrical structure of CCl3+ by trapped-ion electron diffraction

A trapped-ion electron diffraction (TIED) apparatus has been developed. By sufficient suppression of the background signals originating from electrons scattered by residual gases and those originating from the back-scattered and secondary electrons generated at a Faraday cup, the gas electron diffraction pattern of CCl3+, generated through the dissociative ionization of CCl4 by near-IR ultrashort intense laser pulses, is recorded using the TIED apparatus at the electron acceleration voltage of 18.8 keV. The determined internuclear distances, r(C-Cl) = 1.66(2) Å and r(Cl⋯Cl) = 2.87(2) Å, which are consistent with theoretically calculated values, confirm that CCl3+ takes a planar geometry.

Structures of Small Platinum Cluster Anions Ptn-: Experiment and Theory.

The structures of platinum cluster anions - have been investigated by trapped ion electron diffraction. Structures were assigned by comparing experimental and simulated scattering functions using candidate structures obtained by density functional theory computations, including spin-orbit coupling. We find a structural evolution from planar structures (, ) and amorphous-like structures (-) to structures based on distorted tetrahedra (-). Finally, and are based on hcp fragments. While the structural parameters are well described by density functional theory computations for all clusters studied, the predicted lowest energy structure is found in the experiment only for . For larger clusters, higher energy isomers are necessary to obtain a fit to the scattering data.

Structures of Small Tantalum Cluster Anions: Experiment and Theory.

We present a study of the structural evolution of tantalum cluster anions Tan-, 6 ≤ n ≤ 13 using a combination of trapped ion electron diffraction (TIED) experiments with a variety of electronic structure methods. A genetic algorithm has been employed to establish a set of likely structures for each cluster, their geometries and energetics have been studied by density functional theory (DFT), random phase approximation, and two-component (2C) DFT methods, which include spin-orbit coupling. We find octahedral structures for Ta6- and Ta8- as well as structures based on the pentagonal bipyramid (Ta7- and Ta9-). Ta10--Ta12- are defective icosahedral structures and Ta13- is a distorted icosahedron. For most clusters, we find a good agreement between the theoretically predicted ground-state structures, especially those determined by the 2C method and the TIED results.

Structural Phase Transition of Ruthenium Cluster Hydrides

We present a study of the structural effects of hydrogen adsorption on Ru14– investigated by a combination of trapped ion electron diffraction and density functional computations. While the bare Ru...

Structural Evolution of Palladium Clusters Pd55--Pd147-: Transition to the Bulk.

We present a study of the structural evolution of palladium cluster anions in a size range from 55 to 147 atoms using a combination of trapped ion electron diffraction and density functional theory computations. We show that Pdn- clusters (n = 55, 65, 75, 85, 95, 105, and 147) change from an icosahedral motif at Pd55- to the bulk fcc motif at Pd147-. This size-dependent structure transition is probed experimentally at a temperature of 95 K and characterized by a continuously increasing fraction of fcc isomers over the considered size range showing a crossover to the fcc motif at n ≈ 90.

Global optimization of neutral and charged 20- and 55-atom silver and gold clusters at the DFTB level

The global optimization of metallic clusters is an important topic because nanoclusters exhibit structure-dependent properties. In this paper, we present a global optimization study of Ag20, Au20, Ag55 and Au55 in their neutral and charge states (−1, 0, +1) conducted using a Parallel-Tempering Molecular Dynamics algorithm at the DFTB level without pre-screening. For Au20, Ag20 and their ions, the present DFTB low energy structures are in good agreement with previously published calculations and experimental data. In the case of Ag55- and Au55-, the present study is consistent with photo-electron detachment experiments suggesting highly symmetric icosahedral structures for silver and more disordered morphologies for gold. The present results are also compatible with trapped ion electron diffraction experiments and calculations for Ag55+ and Ag55-. We report low-energy isomers of Au55 exhibiting cavities below their external shell. This work quantitatively confirms the relevance of DFTB for structure calculation of noble metal clusters. Furthermore, it also demonstrates the feasibility of global optimization using DFTB, without pre-screening through classical potential, for sizes up to a few tens of atoms and for different charge states.

Ruthenium Cluster Structure Change Induced by Hydrogen Adsorption: Ru19–

The effect of hydrogenation on the structure of Ru19– has been studied using a combination of trapped ion electron diffraction and density functional computations. While the bare Ru19– cluster has a closed-shell octahedral geometry, hydrogenation of the cluster changes the structure type of the ruthenium core toward an icosahedral motif. The experiments show a gradual structural transition depending on the number of adsorbed hydrogen atoms. Density functional theory computations reveal the driving force behind this process to be the larger hydrogen adsorption energies for the bi-icosahedral structure and predict a corresponding structural rearrangement at around 20 adsorbed hydrogen atoms, which is consistent with the experimental findings. Additionally, the computations provide insight into the hydrogen-binding situation. They show that hydrogen is preferentially atomically bound only to surface Ru atoms. H2 binding is predicted only at high hydrogen loadings.

Enantiospecific adsorption of cysteine on a chiral Au34 cluster

The interaction of biological molecules like chiral amino acids with chiral metal clusters is becoming an interesting and active field of research because of its potential impact in, for example, chiral molecular recognition phenomena. In particular, the enantiospecific adsorption (EA) of cysteine (Cys) on a chiral Au55 cluster was theoretically predicted a few years ago. In this work, we present theoretical results, based on density functional theory, of the EA of non-zwitterionic cysteine interacting with the C3-Au34 chiral cluster, which has been experimentally detected in gas phase, using trapped ion electron diffraction. Our results show that, indeed, the adsorption energy of the amino acid depends on which enantiomers participate in the formation Cys-Au34 chiral complex. EA was obtained in the adsorption modes where both the thiol, and the thiol-amino functional groups of Cys are adsorbed on low-coordinated sites of the metal cluster surface. Similarly to what was obtained for the Cys-Au55 chiral complex, in the present work, it is found that the EA is originated from the different strength and location of the bond between the COOH functional group and surface Au atoms of the Au34 chiral cluster. Calculations of the vibrational spectrum for the different Cys-Au34 diastereomeric complexes predict the existence of a vibro-enantiospecific effect, indicating that the vibrational frequencies of the adsorbed amino acid depend on its handedness.

Structural evolution of small ruthenium cluster anions.

The structures of ruthenium cluster anions have been investigated using a combination of trapped ion electron diffraction and density functional theory computations in the size range from eight to twenty atoms. In this size range, three different structural motifs are found: Ru8(-)-Ru12(-) have simple cubic structures, Ru13(-)-Ru16(-) form double layered hexagonal structures, and larger clusters form close packed motifs. For Ru17(-), we find hexagonal close packed stacking, whereas octahedral structures occur for Ru18(-)-Ru20(-). Our calculations also predict simple cubic structures for the smaller clusters Ru4(-)-Ru7(-), which were not accessible to electron diffraction measurements.

Structures of Medium‐Sized Ruthenium Clusters: The Octahedral Motif

We describe the first direct structural characterization of medium-sized ruthenium clusters (Ru19 (-) , Ru28 (-) , Ru38 (-) , and Ru44 (-) ) by using a combination of trapped ion electron diffraction and density functional theory. We find close-packed structures based on octahedral geometries: Ru19 (-) and Ru44 (-) are closed-shell octahedra whereas Ru28 (-) is a double octahedron. In the case of Ru38 (-) , instead of a truncated octahedron we obtain evidence for lower symmetry structures containing a reentrant surface.

Structures of small bismuth cluster cations

The structures of bismuth cluster cations in the range between 4 and 14 atoms have been assigned by a combination of gas phase ion mobility and trapped ion electron diffraction measurements together with density functional theory calculations. We find that above 8 atoms the clusters adopt prolate structures with coordination numbers between 3 and 4 and highly directional bonds. These open structures are more like those seen for clusters of semiconducting-in-bulk elements (such as silicon) rather than resembling the compact structures typical for clusters of metallic-in-bulk elements. An accurate description of bismuth clusters at the level of density functional theory, in particular of fragmentation pathways and dissociation energetics, requires taking spin-orbit coupling into account. For n = 11 we infer that low energy isomers can have fragmentation thresholds comparable to their structural interconversion barriers. This gives rise to experimental isomer distributions which are dependent on formation and annealing histories.

Structures of medium sized tin cluster anions

The structures of medium sized tin cluster anions Sn(n)(-) (n = 16-29) were determined by a combination of density functional theory, trapped ion electron diffraction and collision induced dissociation (CID). Mostly prolate structures were found with a structural motif based on only three repeatedly appearing subunit clusters, the Sn(7) pentagonal bipyramid, the Sn(9) tricapped trigonal prism and the Sn(10) bicapped tetragonal antiprism. Sn(16)(-) and Sn(17)(-) are composed of two face connected subunits. In Sn(18)(-)-Sn(20)(-) the subunits form cluster dimers. For Sn(21)(-)-Sn(23)(-) additional tin atoms are inserted between the building blocks. Sn(24)(-) and Sn(25)(-) are composed of a Sn(9) or Sn(10) connected to a Sn(15) subunit, which closely resembles the ground state of Sn(15)(-). Finally, in the larger clusters Sn(26)(-)-Sn(29)(-) additional bridging atoms again connect the building blocks. The CID experiments reveal fission as the main fragmentation channel for all investigated cluster sizes. This rather unexpected "pearl-chain" cluster growth mode is rationalized by the extraordinary stability of the building blocks.

Structures of tin cluster cations $\rm {Sn_{3}}^+$ Sn 3+ to $\rm {Sn_{15}}^+$ Sn 15+

We employ a combination of ion mobility measurements and an unbiased systematic structure search with density functional theory methods to study structure and energetics of gas phase tin cluster cations, Sn(n)(+), in the range of n = 3-15. For Sn(13)(+) we also carry out trapped ion electron diffraction measurements to ascertain the results obtained by the other procedures. The structures for the smaller systems are most easily described by idealized point group symmetries, although they are all Jahn-Teller distorted: D(3h) (trigonal bipyramid), D(4h) (octahedron), D(5h) (pentagonal bipyramid) for n = 5, 6, and 7. For the larger systems we find capped D(5h) for Sn(8)(+) and Sn(9)(+), D(3h) (tricapped trigonal prism) and D(4d) (bicapped squared antiprism) plus adatoms for n = 10, 11, 14, and 15. A centered icosahedron with a peripheral atom removed is the dominant motif in Sn(12)(+). For Sn(13)(+) the calculations predict a family of virtually isoenergetic isomers, an icosahedron and slightly distorted icosahedra, which are about 0.25 eV below two C(1) structures. The experiments indicate the presence of two structures, one from the I(h) family and a prolate C(1) isomer based on fused deltahedral moieties.

Communications: Tin cluster anions (Snn−, n=18, 20, 23, and 25) comprise dimers of stable subunits

The gas phase structures of tin cluster anions Sn(n)(-) have been studied by a combination of trapped ion electron diffraction and density functional theory calculations. In the size range of n=18-25 these clusters comprise dimers of stable subunits. In particular Sn(18)(-) and Sn(20)(-) are homodimers of Sn(9) and Sn(10) subunits, respectively. In Sn(23)(-) two Sn(10) units are linked by three additional bridging atoms and Sn(25)(-) is a heterodimer of Sn(10) and Sn(15) subunits. This rather unexpected growth mode is rationalized by the extraordinary stability of the building blocks Sn(9), Sn(10), and Sn(15).

Determining the size-dependent structure of ligand-free gold-cluster ions

Ligand-free metal clusters can be prepared over a wide size range, but only in comparatively small amounts. Determining their size-dependent properties has therefore required the development of experimental methods that allow characterization of sample sizes comprising only a few thousand mass-selected particles under well-defined collision-free conditions. In this review, we describe the application of these methods to the geometric structural determination of Au(n)(+) and Au(n)(-) with n = 3-20. Geometries were assigned by comparing experimental data, primarily from ion-mobility spectrometry and trapped ion electron diffraction, to structural models from quantum chemical calculations.

Small tin cluster anions: Transition from quasispherical to prolate structures

The structures and energetics of small tin cluster Sn(n)(-) anions up to n=15 were determined by a combination of density-functional theory and three different experimental methods: Ion mobility spectrometry, trapped ion electron diffraction, and collision induced dissociation. We find compact, quasispherical structures up to n=12. Sn(12)(-) is a slightly distorted hollow icosahedron while Sn(13)(-) to Sn(15)(-) have prolate structures, consisting of merged, hollow, in part incomplete, deltahedral subunits: Sn(13)(-) consists of a face-sharing pentagonal bipyramid and tricapped trigonal bipyramid, Sn(14)(-) comprises a face-sharing dicapped trigonal prism and capped square-antiprism, and Sn(15)(-) consists of two face-sharing tricapped trigonal prisms.

Magnetic doping of the golden cage clusterM@Au16−(M=Fe,Co,Ni)

Structural, electronic, and magnetic properties of the golden cage doped with a transition-metal atom, $M{\text{Au}}_{16}^{\ensuremath{-}}$ ($M=\text{Fe}$,Co,Ni), are investigated using trapped ion electron diffraction, photoelectron spectroscopy, and density-functional theory. The best agreement to experiment is obtained for endohedral $M@{\text{Au}}_{16}^{\ensuremath{-}}$ structures but with considerable distortions to the parent ${\text{Au}}_{16}^{\ensuremath{-}}$ cage. $\text{Fe}@{\text{Au}}_{16}^{\ensuremath{-}}$ and $\text{Co}@{\text{Au}}_{16}^{\ensuremath{-}}$ are found to have similar structures with ${C}_{2}$ symmetry while a ${C}_{1}$ structure is obtained for $\text{Ni}@{\text{Au}}_{16}^{\ensuremath{-}}$. The $4s$ electrons are observed to transfer to the ${\text{Au}}_{16}$ cage, whereas atomiclike magnetism due to the unpaired $3d$ electrons is retained for all the doped clusters.

Structure determination of gold clusters by trapped ion electron diffraction: Au14−–Au19−

The structures of mass-selected gold cluster anions Au(14)(-)-Au(19)(-) have been reinvestigated using an improved low temperature trapped ion electron diffraction experiment. Structures were assigned by comparing experimental with simulated scattering functions using model structures obtained by density functional calculations. Flat three-dimensional structures are found for Au(14)(-) and Au(15)(-), hollow cages for Au(16)(-)-Au(18)(-) and a tetrahedral structure is found for Au(19)(-). For several clusters in this series, our assignments differ distinctly from previous assignments.

Comparative study of the structures of copper, silver, and gold icosamers: Influence of metal type and charge state

We present a comparative study on the structural properties of the coinage metal icosamers Cu(20)(+/-), Ag(20)(+/-), and Au(20)(+/-). Using trapped ion electron diffraction measurements in combination with density functional structure calculations we find distinct structural differences depending on the cluster material and the charge state: Cu(20)(-), Cu(20)(+), as well as Ag(20)(+) prefer icosahedral structures. Ag(20)(-) adopts a rearranged, distorted icosahedral structure. While Au(20)(-) is tetrahedral, Au(20)(+) cannot be described satisfyingly by a single isomer alone. Here a mixture of tetrahedral and distorted icosahedral structures is suggested. The influence of material and charge on the structural properties of the coinage metal icosamers is discussed.

Intrinsic Chirality in Bare Gold Nanoclusters: The Au34− Case

In this work, we provide theoretical evidence on the existence of energetically stable chiral structures for bare gold clusters. Density functional theory calculations within the generalized-gradient approximation were performed to systematically study structural, vibrational, electronic, and optical properties of the lowest-lying isomers of the Au34Z, (Z = +1, 0, −1), clusters. Our results show that for the neutral and charged clusters, the lowest-energy isomer has a C1 (chiral) structure. In addition, a C3 (chiral) isomer was found nearly degenerate in energy with the C1 isomer. These results are in agreement with previous theoretical-experimental studies done for the Au34− cluster; however, because our calculated molecular scattering functions for the C1 and C3 isomers of this cluster are almost indistinguishable, it is concluded that the actual resolution in trapped ion electron diffraction experiments is not enough to discriminate between them. On the other hand, the electronic density of states of t...