Collision processes of size-selected cluster anions, (C₆F₆)_n^- (n = 1-5), with a silicon surface

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.