CRITICAL-BEHAVIOR OF SUPER-HEATED (1900-2000 K) C-60 VAPORS

We report on the experimental observation of a critical phenomenon (ph ase-transition-like) in super-heated C-60 vapours inside an alumina ef fusive oven in the temperature range of 1900-2000 K. This phenomenon i s studied by modulated molecular beam mass spectrometry and the main o bservations are dramatic discontinuous decay of the C-60 flux by a fac tor of similar to 102 within similar to 0.5 K and a simultaneous drama tic rise of a CO+ signal. Nearly complete thermal reversibility is dem onstrated. Under flow conditions with 2-10 Torr helium, Al2O+ and Alare also observed. Both exhibit the same critical behaviour as CO+. Te ntative interpretations are in terms of heterogeneous gas-surface crit ical kinetic phenomena or vapour condensation leading to formation of liquid-like films followed by complete disintegration and oxidation.