Evaluation of ionic mobilities by coupling the scattering on atoms and on electron density

A recently developed method to calculate gas-phase mobilities by scattering on electron density isosurfaces (SEDI) has been applied to carbon cluster ions. The investigation has covered species belonging to all major structur al families identified in drift tube studies (chains, monocyclic and bicycl ic rings, graphite sheets, and fullerenes). Relative cross sections of C-n( -) and C-n(+) predicted by SEDI are in excellent agreement with the measure ments across a wide range of cluster sizes and shapes. However, absolute va lues could not be fit for either charge state. This happens because SEDI ig nores the long-range ion-buffer gas interaction known to be important for m any systems including carbon clusters. To overcome this problem, we propose a new technique to evaluate mobilities by coupling SEDI with trajectory ca lculations. This approach allows one to introduce the repulsive interaction accurately and still account for the attractive part of the potential. Thi s hybrid SEDI-TC treatment has been found substantially superior to all mod els previously described in reproducing both absolute and relative mobiliti es of C-n anions and cations.