Formation of higher-order fullerene dianions in collisions with Na atoms

We have measured electron capture cross sections in collisions between higher order fullerene anions Cn - (n=76, 78, 82, 84, 86, 90 and 96) and Na atoms. The ions were produced in an electrospray ion source (ESI) and accelerated to an energy of 50 keV. The measured cross section for dianion formation is three times larger for C96 than that for C60. The latter cross section was earlier found to be 36 A2. The dramatic increase of the cross section with fullerene size is explained by means of the curve crossing model for electron transfer.