Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Research Reveals Halogen Characteristics

02.04.2004


A stable cluster of aluminum atoms, Al13, acts as a single entity in chemical reactions, demonstrating properties similar to those of a halogen, reports a research team led by A. Welford Castleman Jr., the Evan Pugh Professor of Chemistry and Physics and the Eberly Family Distinguished Chair in Science at Penn State, in a paper to be published in the 2 April 2004 issue of the journal Science. Experimental results and theoretical calculations indicate that the cluster chemically resembles a "superhalogen" atom, retaining its properties during the reaction and in reaction products. Other team members include Denis E. Bergeron of the Penn State departments of chemistry and physics and Shiv N. Khanna of the Virginia Commonwealth University department of Physics. One implication of the research is the possibility of using such clusters as building blocks in nanoscale fabrication.


Figure 1: Charge density map of the highest occupied molecular orbital for the Al13I- cluster. Note the preservation of Al13I- icosahedral geometry, and the localized charge density on the aluminum cluster moiety. Color code: blue=aluminum; red=iodine.


Figure 2: Top Image: Lowest energy structure for Al13I-. Color code: blue=aluminum; red=iodine

Bottom Image: Charge density map of the highest occupied molecular orbital for Al13I-. Color code: blue=aluminum; red=iodine



The project focused on experimental evidence of the existence of a very stable cluster anion, Al13I-, prepared by the gas-phase reaction of aluminum clusters with HI gas. Mass spectrometric analysis indicated that the reaction produced relatively few products, the most abundant corresponding to Al13I-. Energy calculations to determine the bonding mechanism between the aluminum cluster and the iodine atom indicate that the extra electron is localized on the Al13 cluster, meaning that the cluster maintains its integrity throughout the reaction. Because the cluster has a greater electron affinity in the compound, or attraction to the free electron, than does iodine, it can be considered a "superhalogen."

"One of the themes of our research is using the clusters as building blocks for new nanoscale materials," says Castleman. "In many cases, people have worked from the top down; that is, subdividing matter to get it smaller and smaller. We’re trying to work with atoms and molecules and put them together--working our way from the bottom up. If we can retain the properties of aggregates, as we put them together, perhaps we will be able to construct new nanoscale materials." The key to using the aggregates as building blocks is that they retain their individual properties during the reaction and do not coalesce into a large aggregate.


One goal of the research is to test the Jellium model of stable clusters, which treats metal atoms in a small system as positive cores surrounded by the valence electrons. The model predicts certain closed-shell arrangements with high stability, called magic clusters. In the Jellium model, the cluster’s atomic nuclei and inner electrons are seen as a single, spherical, positively charged core, surrounded by valence electrons in electronic shells similar to those of atoms. Essentially, the magic clusters can be viewed as superatoms, capable of forming compounds.

"When we started looking at reactions, Al13 turned out to be a very interesting species for several reasons, " says Castleman. "It behaves very much like a halogen, somewhere between iodine and bromine the way it wants to bind an electron. If we could put an iodine atom in contact with Al133, the Al13 has a little higher electron affinity than iodine, which could allow the Al13 to retain the electron, thereby bonding the Al133 and I together."

Experimental observations indicated that the stability of the Al13I- ion is comparable to that of BrI-, a well-known and very stable molecular halogen ion. The ability of a cluster of aluminum atoms to behave like a halogen opens up the prospect that Al13 and other magic clusters can retain their properties as a building block for assembling new materials.

"This superhalogen is not disrupted even in the presence of the very reactive iodine atom in close proximity, but still keeps its properties," says Castleman. "Now that we have shown that this is possible, we see potential ways to make other clusters, maybe involving other metals or alloys. It should be possible to construct something in the Jellium framework that would have the properties not only of a halogen, but of other types of atoms as well. For example, the Al13- ion itself resembles a rare gas atom because it is so unreactive. Ideally, we could have a whole series of clusters--a ’three dimensional’ periodic table, not of elements but rather of clusters simulating the properties of the elements." The goal is to use these clusters as building blocks to tailor the design and formation of nanoscale materials with selected properties.

This research was supported by the U. S. Air Force Office of Scientific Research and the U. S. Department of Energy.

Barbara K. Kennedy | Penn State
Further information:
http://www.science.psu.edu/alert/Castleman3-2004.htm

More articles from Materials Sciences:

nachricht Researchers devise microreactor to study formation of methane hydrate
23.08.2017 | NYU Tandon School of Engineering

nachricht Meter-sized single-crystal graphene growth becomes possible
22.08.2017 | Science China Press

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

What the world's tiniest 'monster truck' reveals

23.08.2017 | Life Sciences

Treating arthritis with algae

23.08.2017 | Life Sciences

Witnessing turbulent motion in the atmosphere of a distant star

23.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>