Progress towards studying metallocarbohedrenes in the condensed phase

Metallocarbohedrenes (Met-Cars, for short) are molecular clusters of M₈C₁₂ stoichiometry, with M representing one of various early transition metals. Since the 1992 discovery of Met-Cars in the gas phase, numerous molecular beam experiments and theoretical calculations have been conducted in an effort to understand the bonding, geometry, physical, and chemical properties of these unique, metal carbide cage clusters. Despite intense scientific attention, Met-Cars are yet to be isolated. In addition, fundamental issues such as the stability against oxidation and equilibrium geometry are still debatable issues. As a result, the objective of this thesis work was to make progress towards studying Met-Cars in the condensed phase.; Upon evaluation of all reported experimental efforts addressing Met-Car production, a systematic approach was formulated. A reflectron time-of-flight mass spectrometer (TOF-MS) with resolution t/2Δ t ≈ 300 at C₆₀ was constructed for use in the analysis of metallocarbohedrene containing soot. The TOF-MS has been equipped with a direct laser vaporization (DLV) source to study the formation of Met-Cars under “non-clustering” conditions. Thermal and laser desorption analyses can also be conducted. In addition, an arc-discharge source was also built and coupled directly to the mass spectrometer to permit anaerobic mass spectroscopic analysis of the arc-generated soot.; Powder mixtures with an approximate 1:1 molar ratio of the metal of interest and graphite pressed into pellets with an applied load of approximately 4,000 lbs/in2 was found to be necessary to produce Met-Cars. Both Met-Cars and carbon rich metal/carbon clusters could be produced from pellets that were rich in composition with either the metal or carbon species without the characteristic build-up species. Varying the pellet composition could not alter the formation pathway to either species. Laser heating of condensed materials from the DLV production process is shown to produce mass spectra similar to those obtained from molecular beam sources; that is, with the build-up pattern. An optimum laser fluence range was determined using the 532 nm light from a Nd:YAG laser operating at 10 Hz. Accounts on possible formation mechanisms are presented.; Species mass gated at the Met-Car cluster were deposited onto carbon-covered grids and studied using electron diffraction. The species were deposited under hard and soft landing conditions. Under hard landing conditions the Met-Cars and possibly larger M/C clusters undergo atomic rearrangements to produced the metal carbide. Results from the soft landing depositions are inconclusive. The preliminary results are presented.