Structural Identification of Caged Vanadium Doped Silicon Clusters

The geometry of cationic silicon clusters doped with vanadium, ${\mathrm{Si}}_n{\mathrm{V}}^{+}$ ($n=12–16$), is investigated by using infrared multiple photon dissociation of the corresponding rare gas complexes in combination with ab initio calculations. It is shown that the clusters are endohedral cages, and evidence is provided that ${\mathrm{Si}}_{16}{\mathrm{V}}^{+}$ is a fluxional system with a symmetric Frank-Kasper geometry.

Figure 1

IR-MPD spectra (upper traces) of ${\mathrm{Si}}_n{\mathrm{V}}^{+}·\mathrm{Xe}$ complexes ($n=12–15$) and the corresponding computed harmonic vibrational spectra and geometries of the obtained lowest energy isomers of ${\mathrm{Si}}_n{\mathrm{V}}^{+}$ (lower traces). The experimental data points (red crosses) are overlaid with a three-point running average.

Figure 2

IR-MPD spectrum of ${\mathrm{Si}}_{16}{\mathrm{V}}^{+}·\mathrm{Xe}$ (upper trace). The 2nd trace shows the IR spectrum obtained from the MD simulation starting from $\mathbf{i}\mathbf{s}\mathbf{o}\mathbf{1}\mathrm{\text{−}}T$ (red crosses) and a spectrum that is obtained by overlaying the discrete points with a Gaussian profile ($5{\mathrm{cm}}^{-1}$ FWHM) to account for the FELIX linewidth (black line). Computed harmonic vibrational spectra of $\mathbf{i}\mathbf{s}\mathbf{o}\mathbf{1}\mathrm{\text{−}}T$ and $\mathbf{T}\mathbf{S}\mathrm{\text{−}}{T}_d$ are given in the 3rd and 4th traces. Relative energies in eV at the BP86/6-$311+G(d)$ level are given in brackets. The structures shown in the lower trace represent the inner tetrahedral and outer shells of $\mathbf{T}\mathbf{S}\mathrm{\text{−}}{T}_d$ and $\mathbf{i}\mathbf{s}\mathbf{o}\mathbf{1}\mathrm{\text{−}}T$.