Geometric and electronic structure of binary clusters containing silicon atoms

Binary clusters containing silicon atoms such as Si_nNa_m, Si_nC_m, and Si_nF were produced in a molecular beam using laser vaporization. The reactivity of Si_nNa_m toward NO adsorption was found to have an anti-correlation with the ionization energy of Si_nNa_m. The results of ab-initio calculation indicate that on doping with a sodium atom, the electron charge migrates from the sodium atom to the silicon cluster without disturbing seriously the original framework of the silicon cluster. Photoelectron spectroscopy of silicon-sodium cluster anions was conducted using a magnetic bottle type photoelectron spectrometer. The determined electron affinity of Si_nNa was also found to have clear parallelism with the ionization energy of Si_n clusters. This also confirms that the parentage of the singly occupied molecular orbital (SOMO) of Si_nNa is the lowest unoccupied molecular orbital (LUMO) of Si_n. In the case of Si_nF, the electron migrates from the silicon cluster to the fluorine atom, which is reflected clearly in the photoelectron spectra of Si_nF^- clusters. The similarity of the photoelectron spectra of Si_n-1C^- and Si^-_n was attributed to the similarity of their geometric structure (3 ≤ n ≤ 6). In contrast to this, C_n-1Si^- and C^-_n exhibit different photoelectron spectra, indicating the structural difference.