Number 129 (Story #2), May 19, 1993 by Phillip F. Schewe and Ben Stein CLUSTERS OF FULLERENE MOLECULES seem to occur preferentially (but not exclusively) at certain cluster sizes, such as 13, 19, 23, 35, etc. Carbon-60 and Carbon-70 buckyballs are themselves clusters held tightly together. But clusters of buckyballs are only weakly bound by van der Waals forces. A group of scientists at the Max Planck Institute in Stuttgart, Germany have succeeded in ionizing the fragile clusters without breaking them apart and cataloging their hefts in a mass spectrometer (T.P. Martin et al., 11 May 1993 Physical Review Letters). The preferred cluster sizes were similar (but not identical to) those for xenon and argon clusters.