Lanthanum complexes of spheroidal carbon shells

Characterizing cavities in model inclusion molecules: a comparative study

We have selected fullerene-60 and -70 cavities as model systems in order to test several methods for characterizing inclusion molecules. The methods are based on different technical foundations such as a square and triangular tessellation of the molecule taken as a unitary sphere, spherical tessellation of the molecular surface, numerical integration of the atomic volumes and surfaces, triangular tessellation of the molecular surface, and a cubic lattice approach to a molecular space. Accurate measures of the molecular volume and surface area have been performed with the pseudo-random Monte Carlo (MCVS) and uniform Monte Carlo (UMCVS) methods. These calculations serve as a reference for the rest of the methods. The SURMO2 and MS methods have not recognized the cavities and may not be convenient for intercalation compounds. The programs that have detected the cavities never exceed 5% deviation relative to the reference values for molecular volume and surface area. The GEPOL algorithm, alone or combined with TOPO, shows results in good agreement with those of the UMCVS reference. The uniform random number generator provides the fastest convergence for UMCVS and a correct estimate of the standard deviations. The effect of the internal cavity on the accessible surfaces has been calculated.

The chemistry of the interstellar medium

There has been a dramatic advance in our appreciation of the richness of the molecular component of the interstellar medium, mainly brought about by combining laboratory spectroscopic measurements with radioastronomy search programmes. We now know that vast hordes of molecules lurk deep in the black clouds strewn among the stars of the Galaxy. They range from commonplace small species such as water and carbon monoxide through organic ones such as alcohol and formaldehyde to highly reactive ions and free radicals which are intermediates in the production of more complex molecules. The study of the microwave and infrared signals from these molecules has revealed, for the first time, the intimate details that surround the birth of a star. Some intriguing and rather exotic molecules, consisting primarily of carbon atoms connected in long chains, have also been identified. Not only are these curious molecules to be found in the cold tenuous dark clouds but they are also to be found streaming out of carbon-rich stars into the surrounding interstellar medium. Such stars also appear to be emitting copious quantities of dust. Laboratory experiments, stimulated by these observations, have led to the discovery of the hollow spheroidal carbon molecule, C 60 buckminsterfullerene. This discovery has not only provided the key to the mechanism of formation of small carbon particles (such as soot) but also the first detailed understanding of their structure. These processes and the species that result may be directly related to those involved in the formation of the primordial macroscopic particle.

Dreams in a charcoal fire: predictions about giant fullerenes and graphite nanotubes

The early prediction of hollow graphite molecules suggested that they should be supercritical under ambient conditions. This is not true of C 60 , but might still be true of higher fullerenes and graphite nanotubes of large diameter.