The research team, of A. Welford Castleman Jr. and Dasitha Gunaratne from Penn State, and Samuel Peppernick of the Pacific Northwest National Laboratory, found that atoms identified through these mimicry events can be predicted by examining the periodic table.


Published in the Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0911240107), the research used photoelectron-imaging spectroscopy to analyze similarities between titanium monoxide and nickel, zirconium monoxide and palladium, and tungsten carbide and platinum, discovering that the molecules of titanium monoxide, zirconium monoxide, and tungsten carbide are actually superatoms of nickel, palladium, and platinum, respectively.


Castleman worked on aluminum 13 anion clusters many years ago, and realized that they were behaving like composite or unified atoms. Recent studies also explored the behavior of systems comprised of isoelectronic character, which led to the discovery that, in some cases, certain cluster species may display characteristics analogous to individual elements. They discovered that species mimicing various members of the periodic table could be produced, and the terminology of superatoms began to be used.


As Castleman states, “by looking at the periodic table, you can predict that titanium monoxide will be a superatom of nickel. Simply start at titanium, which has four outer-shell electrons, and move six elements to the right, because atomic oxygen possesses six outer-shell electrons. The element you end up on is nickel, whose 10 outer-shell electrons make it isoelectronic with the 10 outer-shell electron molecule resulting from the combination of titanium and oxygen.” They tried the same approach with other atoms, to discover an emerging pattern.


This discovery is providing new insight into the electronic characteristics of isoelectronic materials, and makes possible the tailoring of new materials with desired properties. There is the potential for cluster assembly as a new approach to acquiring new and unique materials with unique electronic properties. The researchers are continuing to examine a wide range of elements of the periodic table to ascertain how fundamental and broadly applicable their discovery is.


The research could mean the introduction of cheaper material in manufacturing; for instance, it could increase the use of tungsten carbide in catalytic converters for automobiles, greatly reducing the costs involved, and the cheaper zirconium monoxide could replace palladium in some combustion processes.