Reactivities of C60C60 and C70C70

We study the reactivities of IhIhC60C60 and D5hD5hC70C70 fullerenes in the framework of the density-functional theory. To quantify the reactivities of fullerenes, we calculate the total energies of the system consisting of a fullerene and a C atom as a function of the distance from each C site on the fullerene surface to the C atom, and obtain the reaction energy defined as energy gain at the minimum-energy configuration from the infinite distance configuration. Surprisingly, it is found that some of the C70C70 sites have larger reaction energies than that of C60C60, although C70C70 is energetically more stable than C60C60. This result sheds new light on the formation process of fullerenes and the abundance of C60C60 in soot.