Zeng-Guang Zhang

Photoelectron spectroscopy and density functional calculations of CuSin− (n = 4–18) clusters

We conducted a combined anion photoelectron spectroscopy and density functional theory study on the structural evolution of copper-doped silicon clusters, CuSi(n)(-) (n = 4-18). Based on the comparison between the experiments and theoretical calculations, CuSi(12)(-) is suggested to be the smallest fully endohedral cluster. The low-lying isomers of CuSi(n)(-) with n ≥ 12 are dominated by endohedral structures, those of CuSi(n)(-) with n < 12 are dominated by exohedral structures. The most stable structure of CuSi(12)(-) is a double-chair endohedral structure with the copper atom sandwiched between two chair-style Si(6) rings or, in another word, encapsulated in a distorted Si(12) hexagonal prism cage. CuSi(14)(-) has an interesting C(3h) symmetry structure, in which the Si(14) cage is composed by three four-membered rings and six five-membered rings.

Smallest fullerene-like silicon cage stabilized by a V2 unit

We conducted a combined anion photoelectron spectroscopy and density functional theory study on V2Si20 cluster. Our results show that the V2Si20 cluster has an elongated dodecahedron cage structure with a V2 unit encapsulated inside the cage. It is the smallest fullerene-like silicon cage and can be used as building block to make cluster-assembled materials, such as pearl-chain style nanowires.

Anion Photoelectron Spectroscopy and Density Functional Study of Small Aluminum-Vanadium Oxide Clusters

Small aluminum-vanadium oxide clusters, AlVO(y)(-) (y = 1-3) and Al(x)VO(2)(-) (x = 2, 3), were investigated with anion photoelectron spectroscopy and density functional calculations. The adiabatic detachment energies of AlVO(y)(-) were estimated to be 1.06 ± 0.05, 1.50 ± 0.08, and 2.83 ± 0.08 eV for y = 1, 2, and 3. Those of Al(2)VO(2)(-) and Al(3)VO(2)(-) were estimated to be 1.22 ± 0.08 and 1.25 ± 0.08 eV. Comparison of theoretical calculations with experimental measurement suggests that the most probable structure of AlVO(-) cluster is quasilinear with O atom in the middle. AlVO(2)(-) has an irregular chain structure of Al-O-V-O and a C(2v) cyclic structure very close in energy. The structure of AlVO(3)(-) cluster is evolved from the C(2v) cyclic AlVO(2)(-) structure by adding the third O atom to the V atom. Al(2)VO(2)(-) has a pair of nearly degenerate Al-O-V-O-Al chain structures that can be considered as cis and trans forms. Al(3)VO(2)(-) probably has two low-lying isomers each containing a four-membered ring. The structures of the corresponding neutral clusters are discussed.

Communications: Investigation of the superatomic character of Al13 via its interaction with sulfur atoms

We investigated Al(n)S(-) (n=3-15) and Al(n)S(2)(-) (n=7-15) clusters with mass spectrometry and photoelectron spectroscopy. We found that Al(13) is relatively robust when it reacts with sulfur atoms, indicating that it has some superatomic character. However, Al(13) cannot be simply considered as a superatom when it interacts with sulfur due to the following reasons: Al(13)s icosahedral structure has been distorted slightly by sulfur atoms; the vertical detachment energies and adiabatic detachment energies of Al(13)S(-) and Al(13)S(2)(-) clusters are not significantly different from those of their neighboring clusters; and the charge distributions in Al(13)S(-) and Al(13)S(2)(-) do not necessarily associate with superatomic behavior of Al(13).

Adsorption of C2H Radical on Cobalt Clusters: Anion Photoelectron Spectroscopy and Density Functional Calculations

We investigated the adsorption of C(2)H radical on small cobalt clusters by mass spectrometry and by measuring the photoelectron spectra of Co(n)C(2)H(-) (n = 1-5) cluster anions. The most stable structures of Co(n)C(2)H(-) (n = 1-5) and their neutrals were determined by comparing the experimental results with theoretical calculations. Our studies show that C(2)H radical still maintains its integrity as a structural unit in Co(n)C(2)H(-) clusters, rather than being divided by Co(n) clusters. The most stable isomers of Co(1-2)C(2)H(-) clusters are linear with the C(2)H interacting with only one Co atom, while those of Co(3-5)C(2)H(-) cluster anions are quasi-planar structures with the carbon-carbon bonds bending slightly toward the Co(3-5) clusters. The carbon-carbon bond of C(2)H is lengthened more in Co(3-5)C(2)H(-) clusters than in Co(1-2)C(2)H(-).

Photoelectron spectroscopy and density functional calculations of FenBO2― clusters

We conducted a study of Fe(n)BO(2)(-) clusters by mass spectrometry and photoelectron spectroscopy. The vertical detachment energies and adiabatic detachment energies of these clusters were evaluated from their photoelectron spectra. We have also performed density-functional calculations of Fe(n)BO(2)(-) (n=1-5) clusters and determined their structures by comparison of theoretical calculations to experimental results. The studies show that BO(2) moiety still maintains its linear structure as the bare BO(2) cluster. BO(2) behaves as a superhalogen. Analysis of molecular orbitals reveals that the highest occupied molecular orbitals of Fe(n)BO(2)(-) clusters are mainly localized on the Fe(n) units.

Structures and Electronic Properties of V3Sin- (n=3-14) Clusters: A Combined Ab Initio and Experimental Study

The anionic silicon clusters doped with three boron atoms, B3Sin- (n = 4-10), have been generated by laser vaporization and investigated by anion photoelectron spectroscopy. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) of these anionic clusters are determined. The lowest energy structures of B3Sin- (n = 4-10) clusters are globally searched using genetic algorithm incorporated with density functional theory (DFT) calculations. The photoelectron spectra, VDEs, ADEs of these B3Sin- clusters (n = 4-10) are simulated using B3LYP/6-311+G(d) calculations. Satisfactory agreement is found between theory and experiment. Most of the lowest-energy structures of B3Sin- (n = 4-10) clusters can be derived by using the squashed pentagonal bipyramid structure of B3Si4- as the major building unit. Analyses of natural charge populations show that the boron atoms always possess negative charges, and that the electrons transfer from the 3s orbital of silicon and the 2s orbital of boron to the 2p orbital of boron. The calculated average binding energies, second-order differences of energies, and the HOMO-LUMO gaps show that B3Si6- and B3Si9- clusters have relatively high stability and enhanced chemical inertness. In particular, the B3Si9- cluster with high symmetry (C3v) stands out as an interesting superatom cluster with a magic number of 40 skeletal electrons and a closed-shell electronic configuration of 1S21P61D102S22P61F14 for superatom orbitals.

Photoelectron spectroscopy and density functional theory study of TiAlOy- (y=1-3) and TiAl2Oy- (y=2-3) clusters

Small titanium-aluminum oxide clusters, TiAlO(y) (-) (y=1-3) and TiAl(2)O(y) (-) (y=2-3), were studied by using anion photoelectron spectroscopy. The adiabatic detachment energies of TiAlO(y) (-) (y=1-3) were estimated to be 1.11±0.05, 1.70±0.08, and 2.47±0.08eV based on their photoelectron spectra; those of TiAl(2)O(2) (-) and TiAl(2)O(3) (-) were estimated to be 1.17±0.08 and 2.2±0.1eV, respectively. The structures of these clusters were determined by comparison of density functional calculations with the experimental results. The structure of TiAlO(-) is nearly linear with the O atom in the middle. That of TiAlO(2) (-) is a kite-shaped structure. TiAlO(3) (-) has a kite-shaped TiAlO(2) unit with the third O atom attaching to the Ti atom. TiAl(2)O(2) (-) has two nearly degenerate Al-O-Ti-O-Al chain structures that can be considered as cis and trans forms. TiAl(2)O(3) (-) has two low-lying isomers, kite structure and book structure. The structures of these clusters indicate that the Ti atom tends to bind to more O atoms.

Structures of manganese polysulfides: mass-selected photodissociation and density functional calculations.

Manganese polysulfide cations, MnS(x)(+) (x = 1-10), were studied with mass-selected photodissociation experiments and density functional calculations. We found that MnS(+), MnS(2)(+) and MnS(3)(+) undergo dissociation at 355 nm by loss of S, S(2) and S(3), respectively. The dissociation of larger clusters is relatively complex because of the existence of multiple isomers and multiple dissociation channels. The geometric structures of the low-lying isomers found by theoretical calculations are consistent with the dissociation channels observed in the experiments. The dissociation of MnS(x)(+) clusters occurs mainly by breaking of the Mn-S bonds since they are weaker than the S-S bonds.

Modification of Reflectron Time-of-Flight Mass Spectrometer for Photodissociation of Mass-Selected Cluster Ions

We introduce a modification of reflectron time-of-flight mass spectrometer for laser photodissociation of mass-selected ions. In our apparatus, the ions of interests were selected by a mass gate near the first space focus point and decelerated right after the mass gate, were then crossed by a laser beam for dissociation. The daughter ions and surviving parent ions were re-accelerated and analyzed by the reflectron time-of-flight mass spectrometer. Compared to the designs reported by other research groups, our selection-deceleration-dissociation-reacceleration approach has better daughter-parent-ions-separation, easier laser timing, and better overlapping between the ion beam and laser beam. We also conducted detailed calculations on the parent ion and daughter ion flight times, and provided a simplified formula for the calibration of daughter ion mass.