The Physics and Chemistry of Clusters (NS 117)

June 27-July 2, 2001
Visby, Gotland, Sweden
Organizers: Professor Mats Larsson, Professor Eleanor E.B. Campbell, Associate Professor Bo Lindgren, Professor Arne Rosén and Associate Professor Ulf Sassenberg

About 65 people participated in the symposium, of whom 26 served as lecturers and about 30 were younger researchers (doctoral students and post-doctoral researchers). The younger researchers presented their contributions at two poster sessions.

Research on the physical and chemical properties of clusters is characterized by very great breadth, extending from highly practical problems to astrophysical riddles. Clusters are aggregations of atoms and molecules with a few to a few thousand components. Clusters therefore, comprise a bridge between single atoms and molecules and condensed phase matter. It is of particular interest to study how cluster properties change depending on how many atoms or molecules the clusters are made of.

The ambition of the symposium was to provide a broad overview of the field, rather than focus on one sub-field. A few lectures dealt with how high-resolution spectroscopic techniques can provide detailed information on the geometric and electronic properties of clusters. One presentation examined how detailed studies of water clusters aim at providing a complete description of water in its liquid phase ("What Makes Water Wet?"). Carbon clusters appear capable of forming "diffuse interstellar bands," which are band structures in the visible spectrum observed in certain astrophysical objects. The origin of these bands has been unkown for more than half a century, but breakthroughs in laboratory studies of carbon clusters seem to provide at least part of the answer.

Clusters can also serve as model systems for chemical reactivities. It is thus possible to "build in" a molecule in a cluster predetermined size, then study the photochemical properties of the system using ultra-fast laser spectroscopy or high-resolution spectroscopy with sharp-frequency lasers. The chemical reactivity properties of clusters may be studied as a function of cluster size, and major variations have been identified. This may later have practical applications, because it has been discovered, for example, that gold clusters have catalytic properties that are absent in solid phase gold. Another practical application of clusters is to use them to modify semiconductor material surfaces. This application appears to have been further developed in Japan than in other countries.

The symposium contributions have been published in book form by World Scientific.