Between the gas phase and the condensed phase of liquids and solids, lies and intermediate state of matter that is not quite one phase or the other. Called clusters, these small agglomerations of atoms and molecules have properties not found in gases or condensed matter. This relatively new field of cluster science has the potential to make important advances in areas as far-reaching as materials science, environmental chemistry, environmental chemistry, catalysis, and biochemistry.
Will Castelman, a chemistry and physics professor at Penn State, has been studying this intermediate state of matter since it was first recognized in the early 1960s. "It started with those of us, in my case, using mass spectrometers to study unique reactions related to the behavior of radioactive materials. I worked for Brookhaven National Laboratory at the time. It was before I even had my Ph.D., but I was running a research group that was looking at radioactive materials in relation to their behavior in possible nuclear accidents. We discovered, looking through the mass spectrometer, that many of the materials were cluster."
A Bowlful of Atoms
Castleman's group began assembling various materials into larger clusters and found some surprising results. Some clusters of atoms began to mimic the behavior of different atoms on the periodic table. "I thought, 'Wow, these are real super atoms,' and I guess it caught on. We thought it was an appropriate name, and most people are now calling them superatoms."