Photoelectron Spectroscopy and Theoretical Study of CrnSi15–n– (n = 1–3): Effects of Doping Cr Atoms on the Structural and Magnetic Properties

Cr _nSi_{15- n}^- ( n = 1-3) clusters were investigated by using size-selected anion photoelectron spectroscopy combined with density functional theory calculations. The results show that the most stable structure of CrSi₁₄^- is of C_{2 v} symmetry with the Cr atom encapsulated in a Si₁₄ cage which can be viewed as a boat-shaped Si₁₀ unit capped by four additional silicon atoms. A large HOMO-LUMO gap of neutral CrSi₁₄ is confirmed based on the photoelectron spectrum of CrSi₁₄^- anion. Cr₂Si₁₃^- has two isomers nearly degenerate in energy: one can be characterized as one Si atom interacting with a Cr₂Si₁₂ hexagonal prism while the other can be viewed as one Si atom capping a distorted Cr₂Si₁₂ hexagonal antiprism. Cr₃Si₁₂^- has a D_{6 d} symmetric wheel structure in which three Cr atoms form an axle surrounded by 12 Si atoms. The magnetic moments of CrSi₁₄^-, Cr₂Si₁₃^-, and Cr₃Si₁₂^- increase from 1 to 3 μB and then to 7 μB with the increasing number of Cr atoms in the clusters. The magnetic moments of Cr₂Si₁₃^- and Cr₃Si₁₂^- are mainly contributed by the surface Cr atoms.