Near thermal energy collisions with fullerenes: a generally applicable soft ionization method for low IP molecules?

Sodium clusters were derivatized via reaction with SF6 or O-2 to generate s upersonic molecular beams containing NaxFy/NaxSFy or NaxO2/NaxO (x less tha n or equal to 10), respectively. These mixed clusters were collided with a C-60 effusive beam at center of mass kinetic energies in the near thermal r egime. Under single collision conditions and in the absence of external lig ht sources, strong cation and anion signals were observed-as detected by ma ss spectroscopy. Signals are due to resonant electron transfer and concomit ant ion pair formation in analogy to previous observations for bare sodium cluster beams. Energetic considerations allow the determination of upper bo unds to the appearance potentials of various mixed cluster cations. Compari son to photoionization mass spectra, indicates that such collisional ioniza tion can be relatively soft and is associated with large cross sections eve n for ionically bound rather than "metallic" electron donors-suggesting tha t the method may be generally applicable for mass spectroscopy of low IP sp ecies. (C) 1999 Elsevier Science B.V.