Collision processes of a size-selected cluster anion, (C6F6)n- (n = 1-5), with a silicon surface were investigated with use of a tandem time-of-flight (TOF) mass spectrometer. The impact of C6F6- on the Si surface at the collision energies of 0-150 eV results in preferential formation of F-, giving a maximum yield at a collision energy of ∼0 eV. This observation can be explained in such a manner that F- is directly produced via the dissociation of C6F6- in an electronically excited state. It is proposed that the electronic excitation of C6F6- upon surface collision proceeds via electron-donation and back-donation processes between C6F6- and the surface. In the low-energy collision of (C6F6)n- (n = 1-5) with the Si surface, the relative yield of C6F5- with respect to F- increases with the size of the parent cluster anion. The formation of F- becomes more favorable in a higher-energy collision of (C6F6)n- (n = 1-5) with the surface. These results lead us to conclude that the solvent molecules are intimately involved in the dissociation of the anionic core in the low-energy collision regime.
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