A. Langenberg

Communication: Highest occupied molecular orbital–lowest unoccupied molecular orbital gaps of doped silicon clusters from core level spectroscopy

A method to determine band gaps of size-selected and isolated nanoparticles by combination of valence band and core-level photoionization spectroscopy is presented. This approach is widely applicable and provides a convenient alternative to current standard techniques for the determination of band gaps by optical or photoelectron spectroscopy. A first application to vanadium doped silicon clusters confirms a striking size-dependence of their highest occupied-lowest unoccupied molecular orbital gaps.

Maximum Spin Polarization in Chromium Dimer Cations as Demonstrated by X‐ray Magnetic Circular Dichroism Spectroscopy

X-ray magnetic circular dichroism spectroscopy has been used to characterize the electronic structure and magnetic moment of Cr2 (+) . Our results indicate that the removal of a single electron from the 4sσg bonding orbital of Cr2 drastically changes the preferred coupling of the 3d electronic spins. While the neutral molecule has a zero-spin ground state with a very short bond length, the molecular cation exhibits a ferromagnetically coupled ground state with the highest possible spin of S=11/2, and almost twice the bond length of the neutral molecule. This spin configuration can be interpreted as a result of indirect exchange coupling between the 3d electrons of the two atoms that is mediated by the single 4s electron through a strong intraatomic 3d-4s exchange interaction. Our finding allows an estimate of the relative energies of two states that are often discussed as ground-state candidates, the ferromagnetically coupled (12) Σ and the low-spin (2) Σ state.

Large orbital magnetic moments of small, free cobalt cluster ions Co n + with n ≤ 9

The size dependent electronic structure and separate spin and orbital magnetic moments of free eo;t (n = 4 9) cluster ions have been invest igated by x-ray ab orption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap. A very large orbital magnetic moment of 1.4 ± 0.1 /.LB per atom was determined for Cot , which is one order of magnitude larger than in the bulk metal. Large orbital magnetic moments per atom of~ 1 /.LB were also determined for CoJ , Cot , and Cot. The orbital contribution to the total magnetic moment shows a non-monotonic cluster sizo dependence: T he orbital contribution increases from a local minimum at n = 2 to a local maximum at n = 5 and then decreases with increasing cluster size. The 3d spin magnetic moment per atom is nearly constant and is solely defined by the number of 3d holes which shows that t he 3d majority ~pin states arc fully occupied , that is, 3d hole spin polarization is 100%. K eywords: orbital magnetic moment, XMCD, cobalt clusters, spin magnetic moment, magnetic anisotropy energy, spin polarization