Geometric and electronic structures of silicon–sodium binary clusters. I. Ionization energy of $SinNam$

Sodium doped silicon clusters (⁠$SinNam;$ $1⩽n⩽14,$ $1⩽m⩽5$⁠) produced by two types of laser vaporization were studied. The adsorption of Na atoms on the $Sin$ clusters leads the substantial lowering of the ionization energy, $Ei,$ of $SinNam$ clusters. Their reactivity toward NO molecules was measured with a fast flow reactor, and the anticorrelation between the $Eis$ and the reactivity was clearly observed; species having low $Ei$ exhibit high reactivity and vice versa. Moreover, the clear parallelism between the $Eis$ of $SinNa$ and the EAs of $Sin$ is found. This is consistent with the fact that the structure of $SinNa$ clusters keeps the frame of the corresponding $Sin$ cluster unchanged and that the electronic structure of $SinNa$ is similar to that of the corresponding negative ion $Sin−.$ In addition to the experimental studies, the geometries, adsorption energies, and vertical ionization energies of $SinNa$ $(n=1–7)$ were investigated with ab initio MO calculations including electron correlation; The Mo/ller–Plesset perturbation theory was used and the configuration interaction (CI) calculation was carried out, particularly for a diatomic molecule, SiNa.