Electron transfer collisions between isolated fullerene dianions and SF6

Electron transfer collisions of trapped doubly charged fullerene anions C76(2-), C(78)2-, and C84(2-) with SF6 are studied in a Fourier transform ion cyclotron resonance mass spectrometer at center-of-mass collisional energies ranging from thermal energy to 77 eV. Collision energy dependencies manifest threshold energies for (nominally exoergic) single electron transfer onto SF6 of 1.46+/-0.3 eV, 1.56+/-0.3 eV, and 1.63+/-0.3 eV for C(76)2-, C78(2-), and C(84)2-, respectively. Kinetics studies reveal charge-transfer cross sections of up to 430+/-200 A2 for C84(2-) at a collision energy of 77 eV. The mechanism and the energetics are discussed in terms of classical electrostatic model calculations. Additionally, we rationalize the collision energy dependencies of the charge-transfer cross sections using the two-state Landau-Zener formalism to describe the associated resonant electron tunneling probability.