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

CrnSi15-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-2v symmetry with the Cr atom encapsulated in a Si-14 cage which can be viewed as a boat-shaped Si-10 unit capped by four additional silicon atoms. A large HOMO-LUMO gap of neutral CrSi14 is confirmed based on the photo-electron 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-6d 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 mu B and then to 7 mu B 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.