Optical and Thermal Properties of Sodium Clusters

The glass-coloring experiments have been performed with gold, silver, nickel and other metals, which are much more difficult to handle theoretically than the alkalis. Among the latter, sodium is the best representative of the nearly free electron gas or jellium model which forms the basic assumption of some of the articles found here. Therefore this review is restricted to sodium clusters, and more specifically to their optical and thermal properties. 

Metal Clusters. Edited by W. Ekardt 1999 John Wiley Sons Ltd 

The present chapter is not written for a complete beginner — more introductory articles can be found in [6-9]. The reader is assumed to be somewhat familiar with the basic notions of the field, like magic numbers, evaporative ensemble, the main features of Jellium theory and so on. 

For the neutral sodium dimer and trimer, beautifully resolved optical spectra are available, which are in excellent agreement with quantum-chemistry-type calculations [10, 11]. The early experiments on larger neutral clusters [12] gave many beautiful results but had one serious drawback. At best it is very difficult to mass-select neutral clusters, so that one has nearly always to work with a broad distribution of masses. In some cases it was possible, nevertheless, to deduce optical data [5, 12]. 

Due to this problem, the experiments are done nearly exclusively today on charged clusters, which were pioneered for the alkalis by the Brechignac group [13, 14]. Only those details of the experiments will be given here that are necessary to understand the results. Many further details can be found elsewhere [9, 13-17]. 

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