NEW EVIDENCE IN FAVOR OF A HIGH (10 EV) C-2 BINDING-ENERGY IN C-60

Time resolved metastable fractions (MFs) for C-2 evaporations from C-n (+) ions (n = 52,54,56,58) were measured on an ion trap/reflectron and modeled using both microcanonical dissociative and radiative decay ra te constants. The concomitant fitting procedure required the use of hi ghly loose transition states with activation entropies, Delta S# - 14- 19 eu. Using the same modeling procedure also allows one to reproduce the major features of previously published breakdown curves for these ions. The present modeling leads also to high C-2 binding energies wit h a value for C-60(+) of Delta E = 9.5 eV. Using a simple thermochemic al cycle leads to a value in slight excess of 10 eV for the binding en ergy of neutral C-60, in excellent agreement with recent ab initio cal culations. (Int J Mass Spectrom 177 (1998) L9-L13) (C) 1998 Elsevier S cience B.V.