Oxidation induced ionization and reactions of metal carbide clusters (Nb, Zr, V, Ta)

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.

Gas-Phase Reactivity of the Ti8C12+ Met-car with Triatomic Sulfur-Containing Molecules: CS2, SCO, and SO2

Gas-phase Ti(x)C(y)+ clusters (x/y = 3/5, 4/7, 5/9, 6/9, 7/12, 8/12, 9/12) including the magic Ti8C12+ (met-car) have been produced by reactive sputtering with a magnetron cluster source. The gas-phase reactivity of the met-car with SCO, CS2, and SO2 was investigated in a hexapole collision cell by way of tandem mass spectrometry. Results indicate an increase in activity as the oxygen-to-sulfur ratio increases (SO2 > SCO > CS2) with products ranging from association to break down of the met-car cluster. Trends in the mass spectra also indicate SCO and CS2 may bond to the met-car in a unique way not observed in previous reactivity studies on Ti8C12+. To investigate this, several possible single molecule-cluster bonding configurations were calculated with density functional theory. The results indicate that bridge bonding of the intact molecules is energetically preferred. In addition, the energy barriers and transition states leading to dissociation products were calculated and the trends are found to be in qualitative agreement with experiment. The effects of the different types of bonding and number of adsorbed species on the reactivity of the met-car along with proposed reaction mechanisms for product formation are also discussed.

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

Niobium and tantalum carbide clusters have been isolated in the gas phase and irradiated with intense tunable infrared (IR) light. Stable neutral clusters are selectively ionized and subsequently detected in a mass spectrometer. By tuning the IR frequency, infrared multiphoton absorption spectra are obtained for a whole range of clusters. These mass-selective IR spectra lead to insights into the structures of small niobium and tantalum carbide clusters and nanocrystals.