Buckyballs: their history and discovery  (Page 2/6)

Above: diamond Below: carbon. Notice how the structure of the two allotropes vary, even though they are bothmade of the same carbon atoms (black)

Diamond and graphite are not the only known allotropes pf carbon, chaoit and carbon(VI), discovered in 1968 and1972, respectively, have also been found. Even more recently, the Buckminsterfullerenes, the subject of this module, were discoveredat Rice by Smalley, Kroto,and Curl. Buckminsterfullerenes is actually a class of allotropes

Above: C540 Below: C60 Both of these are different allotropes of carbon. C60 is the most common and the mostpopularized of the Buckminsterfullerenes. Not shown is the second most common Buckyball, C70 .

In fact, scientists have now discovered hundreds of buckyballs of different sizes, all with the trademarkspherical-like shape. To differentiate them, each allotrope is denoted as C (for carbon) with the number of carbon atoms in thesubscript (i.e. C80). Technically, the geometrical shapes that these buckyballs share are actually known as geodesics, or rather,polyhedrons that approximate spheres. Specifically, the commonly depicted C60 buckyball is a truncated icosahedron. A moresatisfactory representation of it can be had in a soccer ball, with which it shares the exact same shape. It is made up of 12pentagons, each surrounded by 5 hexagons (20 in all).

The discovery

British chemist Harold W. Kroto at the University of Sussex was studying strange chains of carbon atomsfound in space through microwave spectroscopy, a science that studies the absorption spectra of stellar particles billions ofkilometers away to identify what compounds are found in space. This is possible because every element radiates a specific frequency oflight that is unique to that element, which can observed using radiotelescopes. The elements can then be identified because a fundamental rule of matter stating that the intrinsic properties ofelements apply throughout the universe, which means that the elements will emit the same frequency regardless of where they arefound in the universe. Kroto took spectroscopic readings near carbon-rich red giants, or old stars with very large radii andrelatively low surface temperatures, and compared them to spectrum lines of well-characterized substances. He identified the dust tobe made of long alternating chains of carbon and nitrogen atoms known as cynopolyynes, which are also found in interstellar clouds.However Kroto believed that the chains were formed in the stellar atmospheres of red giants and not in interstellar clouds, but hehad to study the particles more closely.

At the same time, Richard Smalley was doing research on cluster chemistry, at Rice University in Houston,Texas. “Clusters” are aggregates of atoms or molecules, between microscopic and macroscopic sizes, that exist briefly. Smalley hadbeen studying clusters of metal atoms with the help of Robert Curl, using an apparatus Smalley had in his laboratory. Thislaser-supersonic cluster beam apparatus had the ability to vaporize nearly any known material into plasma using a laser, which is ahighly concentrated beam of light with extremely high energy.