We report a molecular dynamics simulation of melting and evaporation of the carbon fullerenes ${\mathrm{C}}_{20}$, ${\mathrm{C}}_{60}$, and ${\mathrm{C}}_{240}$. Several phases, among them a previously unknown ‘‘pretzel’’ phase with a three-dimensional structure of multiply connected carbon rings, can be identified above the high initial melting temperature T≊4000 K. At T≳${10}^4$ K, a complete conversion of compact fullerenes to carbon chain fragments is driven by entropy.

• Received 29 November 1993

DOI:https://doi.org/10.1103/PhysRevLett.72.2418