Buckyballs: their history and discovery  (Page 3/6)

Through an acquaintance with Curl, Kroto contacted Smalley and discussed the possibility of using hisapparatus to recreate the high-heat conditions of a red giant’s atmosphere in order to study the clusters of carbon produced, whichmight give Kroto insight as to the formation of the carbon chains. Smalley conceded and Kroto arrived in Smalley’s laboratory in RiceUniversity on September 1, 1985 whom began working on the experiment along with graduate students J.R. Heath and S.C.O’Brien.

Smalley’s apparatus, shown above, fires a high energy laser beam at a rotating disk of graphite in ahelium-filled vacuum chamber. Helium is used because it is an inert gas and therefore does not react with the gaseous carbon. Theintense heating of the surface of the graphite breaks the C—C bonds because of the intense energy. Once vaporized, the carbon atomscool and condense in the high-pressure helium gas, colliding and forming new bond arrangements. Immediately upon cooling severaldegrees above absolute zero in a chamber, the carbon leads to a mass spectrometer for further analysis.

A mass spectrometer uses an atom or molecule’s weight and electric charge to separate it from othermolecules. This is done by ionizing the molecules, which is done by bombarding the molecules with high energy electrons which thenknocks off electrons. If an electron is removed from an otherwise neutral molecule, then the molecule becomes a positively chargedion or cation. The charged particles are then accelerated by passing through electric plates and then filtered through a slit. Astream of charged particles exits the slit and is then deflected by a magnetic field into a curved path. Because all the particles havea charge of +1, the magnetic field exerts the same amount of force on them, however, the more massive ions are deflected less, andthus a separation occurs. By adjusting the strength of the accelerating electric plates or the deflecting magnetic field, aspecific mass can be selected to enter the receptor on the end. After adjusting the experiment, it became greatly evident that themost dominant molecule measured was 720 amu (atomic mass units). By dividing this number by the mass of a single carbon atom (12 amu),it was deduced that the molecule was comprised of 60 carbon atoms (720 / 12 = 60).

The next task was to develop a model for the structure of C60, this new allotrope of carbon. Because it wasoverwhelmingly dominant, Smalley reasoned the molecule had to be the very stable. The preferred geometry for stable molecule wouldreasonably be spherical, because this would mean that all bonding capabilities for carbon would be satisfied. If it were a chain orsheet like graphite, the carbon atoms could still bond at the ends, but if it were circular all ends would meet. Another hint as to thearrangement of the molecule was that there must be a high degree of symmetry for a molecule as stable as C60. Constructing a model thatsatisfied these requirements was fairly difficult and the group of scientists experimented with several models before coming to aconclusion. As a last resort, Smalley made a paper model by cutting out paper pentagons and hexagons in which he tried to stick themtogether so that the figure had 60 vertices. Smalley found that he create a sphere made out of 12 pentagons interlocking 20 hexagonsto make a ball. The ball even bounced. To ensure that the shape fulfilled the bonding capabilities of carbon, Kroto and Curl addedsticky labels to represent double bonds. The resulting shape is that of a truncated icosahedron, the same as that of a soccer ball.Smalley, Curl, and Kroto named the molecule buckminsterfullerene after the American architect and engineer Richard BuckminsterFuller who used hexagons and pentagons for the basic design of his geodesic domes.