Titanium−Carbon Clusters:  New Evidence for High Stability of Neutral Met-Cars

Sakurai, H.; Castleman, A. W.

doi:10.1021/jp970947w

Cited by 21 publications

(10 citation statements)

References 20 publications

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“…In our previous study of the titanium-carbon cluster system, it was established that the mass distribution of the Ti-C clusters is highly dependent on the power of the vaporization laser for cluster formation, and more importantly that the titanium Met-Car, Ti 8 C 12 , is dominantly produced when the vaporization laser power is sufficiently high. 38 Similarly, it was found during the present study that the zirconium and titanium- zirconium mixed Met-Cars were produced abundantly when the vaporization laser power was sufficiently high, while the Met-Car peaks were barely seen at lower vaporization laser powers. Mass spectra of zirconium-carbon and titanium-zirconiumcarbon clusters obtained under the high vaporization laser power conditions are shown in Figure 3.…”

Section: Methodssupporting

confidence: 86%

“…The gas jet, which was composed of a mixture of methane (15% in volume) and helium, was ejected from a pulsed valve (General Valve 99-43-900; a modified version of a standard General Valve Series 9 with a short pulse duration) operated at an absolute stagnation pressure of about 700 kPa. The laser power employed for vaporization in the present experiments was set so that a dominant Met-Car peak was seen in the mass spectra; a detailed description is given later in this section. A fresh metal surface of the metal rod was exposed on each laser shot by a rotational and translational motion controller.…”

Section: Methodsmentioning

confidence: 99%

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Ionization Potentials for the Titanium, Zirconium, and the Mixed Metal Met-Cars

Sakurai

Castleman

1998

J. Phys. Chem. A

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Photoionization spectra of the titanium and zirconium metallocarbohedrene clusters (Met-Cars) of the stoichiometry Ti8 - x Zr x C12 (x = 0−4, 8) have been investigated near threshold. Study of the photoionization efficiencies of these species at different photon energies led to a determination that the ionization potentials (IP's) for the titanium and zirconium Met-Cars, Ti8C12 and Zr8C12, are 4.40 ± 0.02 and 3.95 ± 0.02 eV, respectively. The IP's for the binary metal Met-Cars, Ti8 - x Zr x C12 (x = 1−4), were also determined, and it was found that the IP decreases continuously from that of the pure titanium Met-Car toward that of the pure zirconium Met-Car as the number of substituting zirconium atoms increases.

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Section: Methodssupporting

confidence: 86%

Section: Methodsmentioning

confidence: 99%

Ionization Potentials for the Titanium, Zirconium, and the Mixed Metal Met-Cars

Sakurai

Castleman

1998

J. Phys. Chem. A

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“…Castleman − and Duncan have shown that transition metals such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and Fe all form cagelike structures which have been called metallocarbohedrene (Met-Cars) and that have a stoichiometry of M 8 C 12 where M is the transition metal. As we shall discuss later, the composition of metal−carbon clusters (metallofullerenes, Met-Cars or metal carbides) that are observed in the laser ablation process are very dependent on the experimental conditions.…”

Section: Resultsmentioning

confidence: 99%

Laser Ablation Mass Spectrometry of Pyrolyzed Koppers Coal-Tar Pitch: A Precursor for Fullerenes and Metallofullerenes

et al. 1999

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Pyrolyzed Koppers coal-tar pitch samples consisting mainly of polycyclic aromatic hydrocarbons were studied by direct laser vaporization Fourier transform ion cyclotron resonance and time-of-flight mass spectrometry. Fullerene cations were readily formed from these carbonaceous precursors over a wide range of low-laser ablation power densities. The laser-desorption ionization of the pyrolyzed coal-tar pitches shows the presence of a range of polyaromatic hydrocarbons some containing as many as 70 carbon atoms, which should require only small amounts of laser energy to convert them into fullerenes. Metallofullerene formation also occurs with low power laser ablation of pyrolyzed mixtures of metal oxides, metal sulfides, or metal carbonates and the Koppers coal-tar pitch. Ablation with two different laser pulse widths of 230 µs and 8 ns, at a laser wavelength of 1064 nm, shows that only the long-pulse low-power (200-2000 kW cm -2 ) laser radiation produces metallofullerene ions. The short-pulse high-power (1-2300 MW cm -2 ) laser ablation results only in the formation of small metal carbide cluster and fullerene ions. Collision-induced dissociation experiments were used to study the structures of the small metal carbide clusters and the endohedral metallofullerene ion, La@C 60 + . IntroductionShortly after the discovery of the hollow carbon cage molecules now known as fullerenes, Heath et al. reported that lanthanum atom(s) could be encapsulated in the fullerene cage. 1 The name endohedral metallofullerene written as A m @C 2n , where the symbol @ denotes that the metal atom (A) is located inside fullerene cage and m ) 1-3, n ) 30-70, has been assigned to this new family of fullerenes. 2,3 The novel properties and possible applications of these new molecules as nonlinear optical devices and catalysts, 4 superconductors, 5 lasers, and ferroelectric materials 4,6 have encouraged many researchers to commence macroscale production 3,7-9 and spectroscopic characterization 10-19 of metallofullerenes.Laboratory scale chemical studies on endohedral metallofullerenes are difficult because these species can only be produced with very low yields and so there is a demand for other methods of production or the discovery of new precursors. 20 To date, most of preparations have used graphite/metal or metal oxide mixtures as precursors with different vaporization sources. 8,9,21,22 Our studies on the other hand have been focused on the search for new fullerene and metallofullerene carbon precursors. [22][23][24][25][26][27][28][29][30][31][32][33][34] The use of metal-doped graphite rods with the arc vaporization method 35 and the laser ablation-furnace method 36,37 represent the two major methods for metallofullerene production. Of these two methods, the arc technique is preferred for macroscopic production and yields of less than 0.1% are still common for even the most abundant of the metallofullerenes (for example, La@C 82 ) 38 that can be isolated.

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“…On the other hand, Wei et al produced a series of magic peaks corresponding to the carbon-rich zirconium carbide clusters Zr 13 C 22 + , Zr 18 C 29 + , and Zr 22 C 35 + , Both series of magic numbers therefore seemed associated with separate growth paths selected as a function of the metal−carbon ratio . However, recent investigations carried out by Wang et al on the metal carbide anions provided a quite different distribution of the magic numbers, characterized by the unexpected lack of Ti 8 C 12 - and Zr 8 C 12 - under certain experimental conditions. 8b, The absence of Ti 8 C 12 anions made improbable a double-cage structure for the abundant species Ti 13 C 22 - .…”

Section: Introductionmentioning

confidence: 99%

The Structure and Growth Mechanism of Small Titanium Carbide Clusters: A Competition between C₂and C₄Carbon Chains

et al. 1999

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DFT calculations have been carried out on the titanium carbide clusters Ti 3 C 8 , Ti 4 C 8 , Ti 6 C 13 , and Ti 7 C 13 and their anions, in relation with the recent experimental and theoretical report by L.-S. Wang and his group on those clusters (Wang, L.-S.; Wang, X.-B.; Wu, H.; Cheng, H. J. Am. Chem. Soc. 1998, 120, 6556). The small clusters Ti 3 C 8 and Ti 4 C 8 , characterized by a C/Ti ratio higher than or equal to 2, favor conformations in which the carbon phase is assembled into cis-butadiene-like C 4 chains without bond length alternation. The 19-and 20-atom clusters Ti 6 C 13 and Ti 7 C 13 prefer structures which are reminiscent of the very stable metallocarbohedrene (MetCar) Ti 8 C 12 T d structure. An analysis of the structure most probable for Ti 7 C 13suggests that this conformation cannot be a precursor to multicage clusters. The layer-by-layer growth pathway proposed by Wang et al. therefore appears susceptible to account for the formation and stability of high nuclearity titanium carbide clusters. However, the existence of multicage structures cannot be ruled out with other metals. The surprising absence of the MetCar species Ti 8 C 12and Zr 8 C 12from the mass spectrum of anionic clusters, as observed by Wang under specific experimental conditions, is tentatively explained by the formation of unstable molecular Rydberg states.

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Titanium−Carbon Clusters: New Evidence for High Stability of Neutral Met-Cars

Cited by 21 publications

References 20 publications

Ionization Potentials for the Titanium, Zirconium, and the Mixed Metal Met-Cars

Ionization Potentials for the Titanium, Zirconium, and the Mixed Metal Met-Cars

Laser Ablation Mass Spectrometry of Pyrolyzed Koppers Coal-Tar Pitch: A Precursor for Fullerenes and Metallofullerenes

The Structure and Growth Mechanism of Small Titanium Carbide Clusters: A Competition between C₂and C₄Carbon Chains

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Titanium−Carbon Clusters: New Evidence for High Stability of Neutral Met-Cars

Cited by 21 publications

References 20 publications

Ionization Potentials for the Titanium, Zirconium, and the Mixed Metal Met-Cars

Ionization Potentials for the Titanium, Zirconium, and the Mixed Metal Met-Cars

Laser Ablation Mass Spectrometry of Pyrolyzed Koppers Coal-Tar Pitch: A Precursor for Fullerenes and Metallofullerenes

The Structure and Growth Mechanism of Small Titanium Carbide Clusters: A Competition between C2and C4Carbon Chains

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The Structure and Growth Mechanism of Small Titanium Carbide Clusters: A Competition between C₂and C₄Carbon Chains