Structure determination of gas-phase niobium and tantalum carbide nanocrystals via infrared spectroscopy

Investigation of Structures, Stabilities, and Electronic and Magnetic Properties of Niobium Carbon Clusters Nb7Cn (n = 1-7)

The geometrical structures, relative stabilities, and electronic and magnetic properties of niobium carbon clusters, Nb7Cn (n = 1-7), are investigated in this study. Density functional theory (DFT) calculations, coupled with the Saunders Kick global search, are conducted to explore the structural properties of Nb7Cn (n = 1-7). The results regarding the average binding energy, second-order difference energy, dissociation energy, HOMO-LUMO gap, and chemical hardness highlight the robust stability of Nb7C3. Analysis of the density of states suggests that the molecular orbitals of Nb7Cn primarily consist of orbitals from the transition metal Nb, with minimal involvement of C atoms. Spin density and natural population analysis reveal that the total magnetic moment of Nb7Cn predominantly resides on the Nb atoms. The contribution of Nb atoms to the total magnetic moment stems mainly from the 4d orbital, followed by the 5p, 5s, and 6s orbitals.

Velocity correlated emission of secondary clusters by a single surface impact of a polyatomic ion: A new mechanism of clusters emission and subpicosecond probing of extreme spike conditions

Emission of secondary clusters off clean solid surfaces following impact of a projectile ion at kiloelectronvolt (keV) kinetic energies is important from both the practical and fundamental points of view....

Structural Determination and Bonding Properties of Gas-Phase Ternary [O, Ta, 2C]- Anions

A combined anion photoelectron spectroscopic and quantum chemical investigation was performed to explore the structures and bonding properties of ternary [O, Ta, 2C]^- anions. The atomic bonding connectivity of the ternary anion was found to be (O-Ta-C₂)^- rather than (Ta-O-C₂)^-. The photoelectron spectrum using 266 nm photons was measured, and the theoretical simulated spectrum was calculated, with good agreement between experimental and theoretical results being found. Computations obtained electronic energies and low-energy structures and enabled chemical bonding analyses. The experimental vertical detachment energies of OTaC₂^- were measured to be 2.85 ± 0.08 eV. OTaC₂^- exhibits π aromaticity with two delocalized π electrons and σ antiaromaticity.

The reactivity of Nbn+ clusters with acetylene and ethylene to produce a cubic aromatic metal carbide Nb4C4+

The reactions of niobium cationic clusters with acetylene and ethylene under sufficient gas collision conditions give rise to dominant dehydrogenation and produce a main metal carbide Nb4C4+ which is associated with cubic aromaticity.

Threshold photoionization and density functional theory studies of bimetallic-carbide nanocrystals and fragments: Ta3ZrC(y) (y = 0-4)

Gas-phase bimetallic tantalum-zirconium-carbide clusters are generated using a constructed double ablation cluster source. The Ta(3)ZrC(y) (y = 0-4) clusters are examined by photoionization efficiency spectroscopy to extract experimental ionization energies (IEs). The IE trend for the Ta(3)ZrC(y) cluster series is reasonably similar to that of the Ta(4)C(y) cluster series [V. Dryza et al., J. Phys. Chem. A 109, 11180 (2005)], although the IE reductions upon carbon addition are greater for the former. Complementary density functional theory calculations are performed for the various isomers constructed by attaching carbon atoms to the different faces of the tetrahedral Ta(3)Zr cluster. The good agreement between the experimental IE trend and that calculated for these isomers support a 2x2x2 face centered cubic nanocrystal structure for Ta(4)ZrC(4) and nanocrystal fragment structures for the smaller clusters.

Density-Functional-Theory Studies of the Infrared Spectra of Titanium Carbide Nanocrystals

The infrared (IR) spectra of cuboidic titanium carbide (TiC) nanocrystals have been studied at the density-functional-theory (DFT) level using the Becke-Perdew (BP) functional and triple-zeta quality basis sets augmented by one set of polarization functions (TZVP). The accuracy of the calculations was checked by DFT calculations using the Perdew-Burke-Ernzerhof hybrid functional (PBE0) and up to quadruple-zeta quality basis sets augmented by one set of polarization functions (QZVP). The calculated IR spectrum for Ti(14)C(13) (3 x 3 x 3) is found to be in fair agreement with the experimental IR spectrum obtained by infrared resonance-enhanced multiphoton ionization (IR-REMPI) measurements, whereas, for Ti(18)C(18) (4 x 3 x 3) and Ti(32)C(32) (4 x 4 x 4), the calculated IR spectra differ significantly from the experimental ones. The smallest TiC cluster (Ti(4)C(4), 2 x 2 x 2) considered has not been reported in any mass-spectrometer studies. The present DFT calculations show that the vibrational modes related to the in-plane vibrations of solid TiC are not observed in the IR-REMPI spectra of nanocrystals larger than Ti(14)C(13). Contrary to solid TiC, the studied TiC nanocrystals are nonmetallic with optical gaps of 0.62 eV (0.55 eV) and 0.028 eV (0.027 eV) for Ti(32)C(32) and Ti(108)C(108) (6 x 6 x 6), calculated at the time-dependent density-functional-theory (TDDFT) level using the BP functional. The HOMO-LUMO gaps obtained in the BP DFT calculations are given within parentheses. At the PBE0 DFT level, the HOMO-LUMO gaps for Ti(32)C(32) and Ti(108)C(108) are 1.74 and 0.32 eV, respectively.