T. Bergmann

Evidence for icosahedral shell structure in large magnesium clusters

Abstract Periodic patterns in the mass spectra of (Mg) n for 147 ⩽ n ⩽ 2869 indicate that these clusters have icosahedral symmetry.

Electronic shells and shells of atoms in metallic clusters

Intensity anomalies (magic numbers) have been observed in the mass spectra of sodium clusters containing up to 22 000 atoms. For small clusters (Nan,n≤1500) the anomalies appear to be due to the filling of electronic shells (groups of subshells having the same energy). The shells can be characterized rather well by a pseudoquantum-number, indicating the possible existence of a symmetry higher than spherical. The mass spectra of larger clusters (1500≤n≤22 000) are well explained by the completion of icosahedral or cuboctahedral shells of atoms. The fact that the two types of shells (electron and atom) occur in distinct and non-overlapping size intervals might indicate the existence of a “liquid” to “solid” transition in going from small to large clusters.

Observation of icosahedral shells and subshells in calcium clusters

Abstract The mass spectrum of hot calcium clusters can be characterized as a recurring set of twenty peaks. Each occurrence of the set corresponds to the formation of one icosahedral shell of atoms. Each of the twenty peaks (subshells) within a set (shell) can be correlated to the coverage of one triangular face. Groupings of five faces arranged around a common verstex play a special role in shell formation.

Ionization energies of sodium clusters containing up to 22000 atoms

Abstract Recently it has been shown that the mass spectra of sodium clusters show evidence for magic numbers up to 22000 atoms. In the present investigation we have measured the ionization potential of large sodium clusters. The results indicate that magic numbers observed earlier are caused by an increase in the ionization energy each time a geometric shell of atoms is completed.

Detection of large fullerene clusters

Abstract Large clusters are notoriously hard to detect. Clusters of fullerene molecules containing up to 10000 carbon atoms pose a special problem in that they tend to bounce elastically off the detector. High post acceleration and multiple charging can be used to overcome the problem of detection. Intensity anomalies in the mass spectra of (C 60 ) n and (C 70 ) n indicate that these clusters have a shell structure with icosahedral symmetry.

Calculated electronic properties of medium sized sodium clusters: the inhomogeneous jellium model

Recently observed magic number data for NaN clusters in the size range from 100 to 900 atoms cannot be fully explained by density functional calculations using a homogeneous, spherical positive charge background. However, a centrally compressed spherical background yields steps in the ionization potential at just those magic numbers observed experimentally.

Investigation of large electronic shells in Cs-compound clusters

Magic numbers in cluster mass spectra can be caused by either geometric or electronic structure. The study of metallic compound clusters allows the number of atoms and the number of electrons in clusters to be controlled independently. We report magic numbers in the mass spectra of Cs-compound clusters containing up to 700 free electrons.

Ionization Energies of Large Sodium Clusters: Direct Evidence for Atomic Shell Structure

Recently it has been shown that the mass spectra of sodium clusters show evidence for magic numbers up to 22000 atoms. In the present investigation we have measured the ionization potential of large sodium clusters. The results indicate that magic numbers observed earlier are caused by an increase in the ionization energy each time a geometric shell of atoms is completed.

Subshells, Shells and Supershells in Metal Clusters

In 1949 Maria Goeppert-Mayer1 and Haxel, Jensen and Suess2 suggested a shell model to explain magic numbers of stability for atomic nuclei. Recently, a similar model has been used to sucessfully describe another fermion system — the electrons in metallic clusters3–18.