Critical behaviour of super-heated (1900-2000 K) C-60 vapours

We report on the experimental observation of a critical phenomenon (phase-transition-like) in super-heated C-60 vapours inside an alumina effusive oven in the temperature range of 1900-2000 K. This phenomenon is studied by modulated molecular beam mass spectrometry and the main observations are dramatic discontinuous decay of the C-60 flux by a factor of similar to 102 within similar to 0.5 K and a simultaneous dramatic rise of a CO+ signal. Nearly complete thermal reversibility is demonstrated. Under flow conditions with 2-10 Torr helium, Al2O+ and Al+ are also observed. Both exhibit the same critical behaviour as CO+. Tentative interpretations are in terms of heterogeneous gas-surface critical kinetic phenomena or vapour condensation leading to formation of liquid-like films followed by complete disintegration and oxidation.