STRONG LONG-RANGE FORCES BETWEEN C-60 AND NA ATOMS AND MICROCLUSTERS

We describe a measurement of the long-range van der Waals interaction V = -C6/r(6) between free neutral sodium atoms and clusters (Na-n, 1 l ess than or equal to n less than or equal to 20) and C-60 fullerenes. The C-6 coefficients were derived from absolute integral cross section s for low-energy scattering of a supersonic beam of metal particles by C-60 vapor. Their values are extremely high, ranging from similar to 10(4) a.u. up to more than 10(5) a.u., corresponding to center-of-mass scattering cross sections of up to similar to 6000 Angstrom(2) (which exceeds the hard-sphere dimensions of the particles by a factor of 20 ). These experimental values of C-6 are in excellent quantitative agre ement with the predictions of the London theory of dispersion forces b ased on atom and cluster spectral properties. The strength of the long -range potential is due to high cluster polarizabilities. [S1050-2947( 98)05901-0].