Geometric and electronic structures of silicon–sodium binary clusters. II. Photoelectron spectroscopy of SinNam− cluster anions

Abstract

Electronic properties of silicon–sodium cluster anions (SinNam−; 4⩽n⩽11, 1⩽m⩽3) were investigated by photoelectron spectroscopy using a magnetic-bottle type electron spectrometer. The electron affinities (EAs) of SinNam were determined from the threshold energies in the photoelectron spectra of SinNam−. Besides, the geometries and energies of SinNa− (n=1–7) were investigated with ab initio MO (molecular orbital) calculations; Mo/ller–Plesset perturbation and coupled cluster methods were used to take into account the electron correlation. By an Na adsorption on Sin, the EA decreases for n=4–6, but increases for n⩾7. The calculations for SinNa− show that the Sin framework for n=4–6 accepts at least two excess electrons. For Si7Na−, however, the charge transfer from the Na atom scarcely occurs to avoid distorting the close-packed Si7 framework. Moreover, the ionization energy (Ei) and EA of SinNam show several patterns with the number of the Na atoms, which reflect the charge transfer mechanism in the cluster reflecting the nature of the electron-accepting orbitals of the corresponding Sin and the adsorption types of the Na atoms.