TEMPERATURE-DEPENDENCE OF THE OPTICAL-RESPONSE OF SMALL, OPEN-SHELL SODIUM CLUSTERS

The optical absorption of small, open sodium cluster ions (N-n(+), n = 4, 7, and 11) exhibit an unexpectedly large temperature dependence. C learly separated absorption lines observed for cold clusters (T simila r to 35 K) are interpreted as transitions between electronic states of the Na-n(+) molecule. At the highest temperature (T > 380 K), however , the clusters are liquid, and broad absorption peaks are observed who se energy positions can be explained for n > 7 by the model of nearly free electrons oscillating in a spheroidal container.