Spectroscopic properties of lead hexamer and its ions (Pb6, Pb6+, Pb6−)

Structure and Excitation Spectra of Third-Row Transition Metal Hexafluorides Based on Multi-Reference Exact Two-Component Theory

The structures and some vertical excitation energies of third-row transition metal hexafluorides (MF6, M = Re, Os, Ir, Pt, Au, Hg) were calculated using the generalized-active-space configuration interaction (GASCI) theory based on the exact two-component (X2C) Hamiltonian. The spin-orbit coupling (SOC) was included at the Hartree-Fock level, enabling us to analyze the SOC at the orbital level (spinor-representation). The excitation spectra were assigned based on the double group, a relativistic group theory applicable to states with the SOC. This study provides a fundamental understanding of the ligand field splitting, including the SOC, that is useful for the photochemistry and spin chemistry involving heavy elements.

Exploring the potential energy surface of small lead clusters using the gradient embedded genetic algorithm and an adequate treatment of relativistic effects

Theoretical inclusion of relativistic effects (scalar and spin–orbit) play a crucial role to assure an adequate structural assignment on lead clusters.

Theoretical studies of a 3D-to-planar structural transition in SinAl5−n+1,0,−1(n = 0–5) clusters

A novel ptC structure C₂Al₃⁻which is more stable in energy than the experimentally observed CAl₄^2−.was firstly predicted The C₂Al₃⁻may become a building block to assembly some larger supermolecule containing multiple phC.

Structures of Pb(n) (n = 21-30) clusters from first-principles calculations

Neutral lead clusters Pb(n) (n = 21-30) were studied using a genetic algorithm (GA)/tight-binding (TB) search combined with density functional theory (DFT)-Perdew-Burke-Ernzerhof (PBE) calculations. The calculated results show that the Pb(n) (22 ≤ n ≤ 30) clusters favor endohedral cage structures with two (Pb(22 - 26)) or three (Pb(27 - 30)) endohedral atoms. The binding energies, stabilities, and highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of the Pb(n) clusters were also discussed. The results from our calculations also indicate that Pb(24) and Pb(28) are especially stable clusters compared with their neighbors.

Mass spectrometry and beam deflection studies of tin-lead nanoalloy clusters

Photo-ionization mass spectrometry and electric beam deflection experiments were used to study isolated Sn(M)Pb(N) clusters (7 <or=N + M<or= 13 for tin-rich clusters, 7 <or=N + M<or= 15 for lead-rich clusters) in a molecular beam apparatus. The observed mass spectra reveal a broad abundance distribution of the bimetallic clusters in which all possible cluster compositions can be identified within the investigated size ranges. Comparison of the relative cluster intensities between pure tin or lead clusters (Sn(N+M) and Pb(N+M)) and mixed Sn(M)Pb(N) clusters indicate quite similar relative abundance distributions which can be smoothly shifted from one to the other extreme by changing the composition. The mass spectroscopic findings could be explained by assuming a substitution "alloy" formation in the Sn(M)Pb(N) cluster system. In combination, the dielectric properties were determined by passing the bimetallic clusters through an inhomogeneous electric field. The observed polarizabilities are significantly increased for most of the bimetallic clusters. This can be explained in an adiabatic polarization model by the presence of permanent electric dipole moments. These observations demonstrate how the electronic properties are not only crucially influenced by the cluster size but also by the composition of this nanoalloy model system. In addition to the enhanced polarizability, most of the measured beam profiles for tin-rich clusters show detectable beam broadenings due to the permanent dipole moments, in contrast to lead-rich clusters which possess considerable smaller dipole moments. Molecular dynamic simulations of the measured beam profile for Sn(6)Pb(1) taking theoretically calculated isomeric structures and dipole moments into account yields no completely satisfying outcome. Therefore we discuss possible reasons for the discrepancy between experimental and theoretical results.

Atomic and electronic structures of neutral and charged Pbn clusters (n=2–15): Theoretical investigation based on density functional theory

The geometric and electronic structures of the Pbn+ clusters (n=2-15) have been investigated and compared with neutral clusters. The search for several low-lying isomers was carried out under the framework of the density functional theory formalism using the generalized gradient approximation for the exchange correlation energy. The wave functions were expanded using a plane wave basis set and the electron-ion interactions have been described by the projector augmented wave method. The ground state geometries of the singly positively charged Pbn+ clusters showed compact growth pattern as those observed for neutrals with small local distortions. Based on the total energy of the lowest energy isomers, a systematic analysis was carried out to obtain the physicochemical properties, viz., binding energy, second order difference in energy, and fragmentation behavior. It is found that n=4, 7, 10, and 13 clusters are more stable than their neighbors, reflecting good agreement with experimental observation. The chemical stability of these clusters was analyzed by evaluating their energy gap between the highest occupied and lowest unoccupied molecular orbitals and adiabatic ionization potentials. The results revealed that, although Pb13 showed higher stability from the total energy analysis, its energy gap and ionization potential do not follow the trend. Albeit of higher stability in terms of binding energy, the lower ionization potential of Pb13 is interesting which has been explained based on its electronic structure through the density of states and electron shell filling model of spherical clusters.

Pbm−Phenyl (m = 1−5) Complexes: an Anion Photoelectron Spectroscopy and Density Functional Study

The phenyl-lead metal complexes ([Pb(m)C6H5]-) produced from the reactions between benzene and lead clusters formed by laser ablation on a lead solid sample are studied by photoelectron spectroscopy (PES) and density functional theory (DFT). The adiabatic electron affinities (EAs) of [Pb(m)C6H5]- are obtained from PES at 308 nm, and the differences between the PES of [Pb(m)C6H5]- and the PES of Pbm- are discussed in detail. The results reveal that the phenyl group binds perpendicularly on lead clusters through the Pb-C sigma bond and the complexes have a closed shell structure. Calculations with DFT are carried out on the structural and electronic properties of [Pb(m)C6H5]-, and the adiabatic detachment energy for the optimized structures of anion are in agreement with the experimental PES results. The density of states (DOS) calculated is compared with experimental PES and is discussed. The most possible structures for each species are concluded, and the bonding between Pb and phenyl is analyzed, which also proves that the phenyl group binds perpendicularly on lead clusters through the Pb-C sigma bond.

Spectroscopic properties of novel aromatic metal clusters: NaM4 (M=Al,Ga,In) and their cations and anions

The ground- and several excited states of metal aromatic clusters, namely NaM(4) and NaM(4) (+/-) (M=Al,Ga,In) clusters have been investigated by employing complete active-space self-consistent-field followed by multireference singles and doubles configuration interaction computations that included up to 10 million configurations and other methods. The ground states NaM(4) (-) of aromatic anions are found to be symmetric C(4nu) ((1)A(1)) electronic states with ideal square pyramid geometries. While the ground state of NaIn(4) is also predicted to be a symmetric C(4nu) ((2)A(1)) square pyramid, the ground state of the NaAl(4) cluster is found to have a C(2nu) ((2)A(1)) pyramid with a rhombus base, and the ground state of NaGa(4) possesses a C(2nu) ((2)A(1)) pyramid with a rectangle base. In general, these structures exhibit two competing geometries, viz., an ideal C(4nu) structure and a distorted rhomboidal or rectangular pyramid structure (C(2nu)). All of the ground states of the NaM(4) (+) (M=Al,Ga,In) cations are computed to be C(2nu) ((3)A(2)) pyramids with rhombus bases. The equilibrium geometries, vibrational frequencies, dissociation energies, adiabatic ionization potentials, adiabatic electron affinities for the electronic states of NaM(4) (M=Al,Ga,In), and their ions are computed and compared with experimental results and other theoretical calculations. On the basis of our computed excited states energy separations, we have tentatively suggested assignments to the observed X and A states in the anion photoelectron spectra of Al(4)Na(-) reported by Li et al. [X. Li, A. E. Kuznetov, H. F. Zheng, A. I. Boldyrev, and L. S. Wang, Science 291, 859 (2001)]. The X state can be assigned to a C(2nu) ((2)A(1)) rhomboidal pyramid. The A state observed in the anion spectrum is assigned to the first excited state ((2)B(1)) of the neutral NaAl(4) with the C(4nu) symmetry. The assignments of the excited states are consistent with the experimental excitation energies and the previous Green's function-based methods for the vertical transition energy separations between the X and A bands.