SURFACE SCATTERING OF C-60- RECOIL VELOCITIES AND YIELD OF C-60( )

In the impact of a C60+ beam against solid surfaces, a substantial fra ction of the beam is neutralized. By means of a pulsed photoionization experiment, we have detected the neutralized scatterers from a silico n (100) surface, and found that they are mainly intact C60, with littl e or no fragmentation at impact energies to 200 eV. The neutralization probability is found to increase monotonically with increasing impact energy. This reionization method has been used in a time-of-flight sc heme to measure the recoil velocity distributions of scattered C60. Co llisions at impact energies above 50 eV are found to be highly inelast ic, and the normal recoil distribution changes very little with impact energy over the range from 50 to 200 eV. The peak in the velocity dis tribution is near 1150 m/s (approximately 5 eV), with a full width at half-maximum (FWHM) of 350 m/s. By comparison with molecular dynamics simulations, an interpretation of this speed is proposed in terms of a limit to reversible deformation of the fullerene cage. A model of the scattering kinematics, based on treating the fullerene cage as a defo rmable, hollow sphere, with a harmonic deformation limit (15 eV) as fo und by theory, predicts the observed speed quantitatively.