Thermal stability of $\rm C_{60}$ and $\rm C_{70}$ fullerites

The thermal properties of $\rm C_{60}$ and $\rm C_{70}$ fullerenes and fullerites have been studied via X-ray structural analysis and UV spectroscopy. It was shown that $\rm C_{70}$ fullerite is stabler than $\rm C_{60}$ fullerite (by $\sim150^{\circ}$C) due to the different geometry of the fullerenes and stronger intermolecular interactions. The experimental results are given a qualitative and quantitative interpretation based on the calculation of the interaction energy between two fullerene molecules.