Ion-pair formation in near-thermal energy collisions of sodium clusters with electron acceptors

Sodium clusters (Nax, x⩽100) were collided with A=TCNQ, C84, C60, Br2, or SF6 at near-thermal energies under crossed beam conditions. Efficient single collisional ionization was observed for all A. Resulting cations and anions were studied by mass spectroscopy. Resonant electron transfer followed by charge separation to yield parent cluster cation (Nax+*) and anion (A−*) pairs is an important channel—given sufficient center of mass kinetic energy. It is the only charging process observed for the fullerenes and TCNQ. For Br2 and SF6, electron transfer can give rise to either charge separation or bond rearrangement/chemi-ionization. We discuss factors influencing the energetics, inelasticity, and probability of electron transfer/ion-pair formation in these systems.