Transition metal clusters mass spectra

At the same time cis Smalley and students at Rice University, Houston Texas, developed the laser vaporization method for production of clusters [84], a similar set-up was built at Exxon s Research Laboratory, New Jersey, USA, by the group of Kaldor and Cox [102,103]. They studied in particular transition metal clusters but also produced clusters of carbon containing up to more than hundreds of atoms as shown in the mass spectrum in Fig. 12. 

Similar experiments on a large number of transition metal carbonyls have shown that this process favors dissociation to and detection of metal clusters or atoms. Since most metal-(CO)n photofragments are themselves subject to efficient dissociation, MPI experiments do not identify the primary photoproducts. This situation contrasts sharply with electron impact ionization where the parent ion is usually formed and daughter ions are seen as a result of parent ion fragmentation. Figure 4 shows the electron impact mass spectrum of Mn2(C0) Q (33). for comparison with the MPI mass spectrum of Figure 3. 

Elements with distinctive isotope ratios (Cl, Br, and transition metals, for example) will provide a distinctive isotopic cluster in the mass spectrum of a compound. This can be used to identify the presence of elements within unknown compounds. 

Chelation of copper with tetraphenylporphyrin was first reported as a technique for measuring copper in rat brain by isotope dilution O) This method appeared to be adaptable for measurement of isotopic enrichment in other biological samples Tetraphenylporphyrin reacts quickly and quantitatively to form chelates with nearly all of the transition metals (M The mass spectrum of a TPP chelate is dominated by the molecular ion cluster (Figure 1) the molecular ion is also the base peak so it is well-suited for quantitation of isotope ratios ... 

In summary, ionisation potentials, dissociation and cohesive energies for mercury clusters have been determined. The mass spectrum of negatively charged Hg clusters is reported. The influence of the transition from van der Waals (n < 13), to covalent (30 < n < 70) to metallic bonding (n > 100) is discussed. A cluster is defined to be metallic , if the ionisation potential behaves like that calculated for a metal sphere. The difference between the measured ionisation potential and that expected for a metallic cluster vanishes rather suddenly around n 100 Hg atoms per cluster. Two possible interpretations are discussed, a rapid decrease of the nearest-neighbour distance and/or the analogue of a Mott transition in a finite system. Electronic correlation effects are strong they make the experimentally observed transitions van der Waals/covalent and covalent/metallic more pronounced than calculated in an independent electron theory. 

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