More Magic Numbers in Titanium-Carbon Anion Clusters: Can This Be Explained by Any Structural Growth Pattern?

Titanitum-carbon anion clusters with a mass range up to 1800 amu have been generated in a Smalley-type cluster source involving a target rod composed of titanium and graphite powders, and have been analysed by time-of-flight mass spectrometry. In the lower mass range (up to 1200 amu), our mass spectrum reproduces all the magic numbers, which have been reported previously, i.e. Ti_(3)C_(8)^(-), Ti_(6)C_(13)^(-), Ti_(7)C_(13)^(-), Ti_(9)C_(15)^(-), Ti_(13)C_(22)^(-), and Ti_(14)C_(24)^(-), in spite of many differences in experimental conditions. In the higher mass range (1200-1800 amu), we observe new magic numbers at Ti_(15)C_(26)^(-), Ti_(20)C_(33)^(-)/Ti_(20)C_(34)^(-) and Ti_(25)C_(42)^(-), which cannot be accounted for by the previously proposed structural growth patterns. All the magic and local maximum Ti_(x)C_(y) peaks have a metal-to-carbon ratio of approximately 1:1.7. The present results suggest a further complexity to the structural growth patterns of the transition metal-carbon mixed cluster systems.

Observation of Electronic Shells and Characteristic Products from Mass Abundance Spectra of Al Cluster and Al-C Cluster Anions

Using a laser vaporization/pulsed molecular beam cluster source,Al cluster anions and Al-C mixed cluster anions are produced and recorded by a time of flight mass spectrometer.Mass abundance spectra of the Al cluster anions in the size range from Al_(2)^(-)to Al_(42)^(-)show that Al_(13)^(-),Al_(23)^(-),Al_(35)^(-),and slightly,Al_(37)^(-)are local maxima,as predicted by the electronic jellium model.Mixed clusters Aln C-and Aln C_(2)^(-)are also shown,among which the most abundant species are Al3 C2,Al6 C_(2)^(-),A_(l7)C^(-)and A_(l7)C_(2)^(-)in the small size range.The formation mechanism of these products is discussed.

Two Types of Mass Abundance Distributions for Anionic Carbon Clusters Investigated by Laser Vaporization and Pulsed Molecular Beam Techniques

Two types of mass spectra for anionic carbon clusters Cn have been revealed using laser vaporization and pulsed molecular beam techniques.The less structured mass spectrum characteristic of the magic-numbers at n=5,8,",15,and 17 is established at the early stage of the cluster formation process,namely,in the laser vaporization,process.The more structured one is featured for a regular odd-even alternation and the magic numbers at n=IO,12,16,18j 22j and 28,and has been developed only after extensive clustering and qnenching processes,where low-energy electron attachment plays a vital role.Transition between these two types of mass spectra can be realized by controlling either the strength of the pulsed gas flow or the synchronism between the gas How and the laser vaporization.

Photoionization Time-of-Flight Mass Spectra of Aluminum Clusters-Associated Complexes

Using a laser vaporization/pulsed molecular beam source,photoionization time-of-flight mass spectra of bare aluminum clusters Aln(n up to larger than 70)and of carbon-,oxygen-,and hydrogen-adducted aluminum clusters-associated complexes are detected.The cause of the observed odd-even alternation in reactivity of Aln and the formation mechanism of the informative products are discussed.

Role of Cluster Geometry in Evolution of Electronic Structures of Small Aluminum Clusters

The electronic structures of small aluminum clusters,Al_(n)(n=5-24),are investigated by a localized-orbital theory based on the tight-binding approximation.Magic-numbered clusters each exhibit a HOMO-LUMO gap maximum,and simultaneously an s-p gap minimum,but not necessarily an ionization potential maximum,where HOMO-LUMO gap denotes the energy gap between the highest occupied orbital and the lowest unoccupied orbital of the cluster.Also revealed is an irregular odd-even alternation in HOMO-LUMO gaps for Al_(n)(n=7-24).Cluster geometry either contributes to or dominates these findings.

Photoionization Mass Spectrometric Study of Neutral Bare Aluminum Clusters and Aluminum-Carbon Mixed Clusters

Photoionization time of flight mass spectra of bare aluminum and aluminum-carbon mixed clusters as well as a variety of oxygen-and oxygen-carbon-adducted aluminum clusters are recorded and assigned.The discontinuities in the mass abundance spectra at AI_(7),AI_(13),AI_(23),AI_(7)C,AI_(13)C,and AI_(24)C are revealed.The findings are interpreted in terms of the electronic and geometric structures of these species.

Characterization of Mass Spectra of Aluminum Anion Clusters Generated by Laser Vaporization and Pulsed Molecular Beam Techniques

Aluminum anion clusters are generated by laser vaporization and molecular beam techniques.Mass abundance spectra exhibit a pronounced odd-even alternation for clusters ranging from n=5 to n=17,which is related to the presence of trace oxygen and water resident in He carrier gas and explained by electron pairing effects.In addition,confirmation of jellium model predictions is revealed at peaked A113-,and for the first time at Al_(7)O^(-).A local maximum Al7-is also observed.