Sheng-Jie Lu

Probing the structural evolution of ruthenium doped germanium clusters: Photoelectron spectroscopy and density functional theory calculations.

We present a combined experimental and theoretical study of ruthenium doped germanium clusters, RuGen− (n = 3–12), and their corresponding neutral species. Photoelectron spectra of RuGen− clusters are measured at 266 nm. The vertical detachment energies (VDEs) and adiabatic detachment energies (ADEs) are obtained. Unbiased CALYPSO structure searches confirm the low-lying structures of anionic and neutral ruthenium doped germanium clusters in the size range of 3 ≤ n ≤ 12. Subsequent geometry optimizations using density functional theory (DFT) at PW91/LANL2DZ level are carried out to determine the relative stability and electronic properties of ruthenium doped germanium clusters. It is found that most of the anionic and neutral clusters have very similar global features. Although the global minimum structures of the anionic and neutral clusters are different, their respective geometries are observed as the low-lying isomers in either case. In addition, for n > 8, the Ru atom in RuGen−/0 clusters is absorbed endohedrally in the Ge cage. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. The excellent agreement between DFT calculations and experiment enables a comprehensive evaluation of the geometrical and electronic structures of ruthenium doped germanium clusters.

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.

Structures and electronic properties of B2Si6−/0/+: anion photoelectron spectroscopy and theoretical calculations

We measured the photoelectron spectrum of B2Si6− anion and investigated the structures and electronic properties of B2Si6− anion as well as those of its neutral and cationic counterparts with quantum chemical calculations. The vertical detachment energy (VDE) of the B2Si6− anion has been measured to be 2.40 ± 0.08 eV. Through global minimum searches and CCSD(T) calculations, we have identified that the lowest-energy structures of B2Si6q (q = −1, 0, +1) are peculiar structures with a Si atom hanging over a distorted bowl-like B2Si5 framework. Quasi-planar or planar isomers have also been identified for the B2Si6 cluster at −1, 0, and +1 charge states. The quasi-planar and planar isomers are higher in energy than their bowl-like counterparts by at least 0.20 eV. The symmetries of the quasi-planar isomers varied at different charge states, ranging from Cs to C2h, then to D2h respectively for the −1, 0, and +1 charge states. The reducing of the symmetry from +1 charge state to −1 charge state is more likely due to the Jahn–Teller effect upon the addition of electrons.

Spin–Orbit Splittings and Low-Lying Electronic States of AuSi and AuGe: Anion Photoelectron Spectroscopy and ab Initio Calculations

We measured the photoelectron spectra of diatomic AuSi- and AuGe- and conducted calculations on the structures and electronic properties of AuSi-/0 and AuGe-/0. The calculations at the CASSCF/CASPT2 level confirmed that experimentally observed spectra features of AuSi- and AuGe- can be attributed to the transitions from the 3Σ- anionic ground state to the 2Π (2Π1/2 and 2Π3/2), 4Σ-, 32Σ+, and 42Σ+ electronic states of their neutral counterparts. The electron affinities (EAs) of AuSi and AuGe are determined by the experiments to be 1.54 ± 0.05 and 1.51 ± 0.05 eV, respectively. The spin-orbit splittings (2Π1/2-2Π3/2) of AuSi and AuGe measured in this work are in agreement with the literature values. The energy difference between the 4Σ- (A) and 2Π1/2 states of AuSi obtained in this work is in reasonable agreement with the literature value, while that of AuGe obtained in this work by anion photoelectron spectroscopy is slightly larger than the literature value by neutral emission spectroscopy. The term energies of the 32Σ+ (B) and 42Σ+ (C) states of AuSi and AuGe were also determined based on the photoelectron spectra. Because of the different bond lengths between the anionic and neutral states, the electronic state terms energies of AuSi and AuGe estimated from the anion photoelectron spectra might be slightly different from those obtained from the neutral emission spectra.

Structural evolution and bonding properties of Au2Sin−/0 (n = 1–7) clusters: Anion photoelectron spectroscopy and theoretical calculations

The photoelectron spectra of Au2Sin- (n = 1-7) clusters were measured, and the structural evolution and bonding properties of Au2Si1-7- anions and their corresponding neutral counterparts were investigated by theoretical calculations. The two Au atoms in Au2Si1-7-/0 prefer to occupy low coordinate sites and form fewer Au-Si bonds. The aurophilic interaction is fairly weak in these clusters. The most stable structures of both Au2Sin- anions and Au2Sin neutrals can be described as the two Au atoms interacting with the Sin frameworks. The most stable isomers of Au2Sin- anions are in spin doublet states, while those of the neutral clusters are in spin singlet states. The lowest-lying isomers of Au2Si1-/0 have C2v symmetric V-shaped structures. The global minimum of the Au2Si2- anion has a D2h symmetric planar rhombus structure, while that of the Au2Si2 neutral adopts a C2v symmetric dibridged structure. In Au2Si3-/0, the two Au atoms independently interact with the different Si-Si bonds of the Si3 triangular structure. The global minima of Au2Si4-7-/0 primarily adopt prismatic based geometries. Interestingly, Au2Si6-/0 have significant 3D aromaticity and possess σ plus π double bonding characters, which play important roles in their structural stability.

The structural and electronic properties of NbSin−/0 (n = 3–12) clusters: anion photoelectron spectroscopy and ab initio calculations

Niobium-doped silicon clusters, NbSin- (n = 3-12), were generated by laser vaporization and investigated by anion photoelectron spectroscopy. The structures and electronic properties of NbSin- anions and their neutral counterparts were investigated with ab initio calculations and compared with the experimental results. It is found that the Nb atom in NbSin-/0 prefers to occupy the high coordination sites to form more Nb-Si bonds. The most stable structures of NbSi3-7-/0 are all exohedral structures with the Nb atom face-capping the Sin frameworks. At n = 8, both the anion and neutral adopt a boat-shaped structure and the openings of the boat-shaped structures remain unclosed in NbSi9-10-/0 clusters. The most stable structure of the NbSi11- anion is endohedral, while that of neutral NbSi11 is exohedral. The global minima of both the NbSi12- anion and neutral NbSi12 are D6h symmetric hexagonal prisms with the Nb atom at the center. The perfect D6h symmetric hexagonal prism of NbSi12- is electronically stable as it obeys the 18-electron rule and has a shell-closed electronic structure with a large HOMO-LUMO gap of 2.70 eV. The molecular orbital analysis of NbSi12- suggests that the delocalized Nb-Si12 ligand interactions may contribute to the stability of the D6h symmetric hexagonal prism. The AdNDP analysis shows that the delocalized 2c-2e Si-Si bonds and multicenter-2e NbSin bonds are important for the structural stability of the NbSi12- anion.