MEASUREMENT OF THE 2ND-ORDER MOLECULAR HYPERPOLARIZABILITY OF FULLERENE ANIONS BY CARS SPECTROSCOPY

We have determined the second-order molecular hyperpolarizability, gam ma, for the fullerene anions C-60(2-) and C-60(3-) by use of coherent anti-Stokes Raman spectroscopy (CARS) vibrational lineshape analysis, We observe values that are only 2-3-times greater than the correspondi ng value for the singly charged anion C-60(-). The behavior of gamma w ith the addition of charge is explained by symmetry considerations, Co mparison with similar results for rare earth-containing endohedral ful lerenes suggests that increased charge on the cage, and not asymmetric charge distribution due to metal-cage interactions, is the primary re ason for increased nonlinearity compared to neutral fullerenes. (C) 19 98 Elsevier Science B.V. All rights reserved.