Electronic properties of silicon-carbon and silicon-sodium binary clusters, produced by laser vaporization, were investigated by photoelectron spectroscopic or photoionization spectroscopic method. The photoelectron spectra of the C1Sim-1- clusters are similar to those of pure Sim- clusters in the peak positions and their envelopes, which is attributed to the similar electronic structure of Si and C atoms, leading to a similar geometry. In contrast, the similarity in the photoelectron spectra is not observed between Cn- and Cn-1Si1 clusters, which is attributed to a change in their geometry; from chain to ring.
The ionization energies (Ei) of the SinNam clusters (l≤n≤15) were determined from the threshold energy of their ionization efficiency curves. The clear parallelism between the ionization energy of SinNa and the electron affinity (EA) of Sin is found; there are three local minima at n=4, 7 and 10. This implies the facts that (1) the structure of the SinNa clusters keeps the frame of the corresponding Sin cluster unchanged and that (2) the parentage of singly occupied molecular orbital (SOMO) of SinNa is the LUMO of Sin. Furthermore, the EAs of SinNa (4≤n≤7) were determined from the threshold energy in the photoelectron spectra of SinNa". When the EAs of SinNa are compared with those of Sin, the EAs decrease at n=4-6, but the EA increases at n=7. The results of ab initio calculation show that the Na atom is bound by two Si atoms (bridge site) at n=4-6, whereas it is bound by one Si atom (apex site) at n=7.