C2 binding energy in C60

This article reviews, on the basis of mass spectrometric experiments, the current status concerning the C-2 binding energy or evaporation energy in C-60, D(C-58-C-2)= Delta E-vap(C-60). Kinetic energy release distributions, time-resolved metastable fractions, breakdown curves, and thermionic emission rates all point to Delta E-vap(C-60(+)) greater than or equal to 9.5 eV and Delta E-vap(C-60) greater than or equal to 10 eV. These results are in agreement with high-level ab initio density functional theory calculations and with expectations from the known heats of formation of C-60, C-70, and C-2. The C-2 evaporation is characterized by a very loose transition state with a pre-exponential factor close to the calculated upper limit. (C) 2000 Elsevier Science B.V.