TEMPERATURE EFFFECTS IN ANION PHOTOELECTRON SPECTROSCOPY OF METAL CLUSTERS

摘要

Dramatic temperature effects were observed in photoelectron spectra of aluminum clusters. For cold clusters, well-defined spectral features representing the energy levels of the clusters were revealed while hot clusters gave much broader spectra under the same experimental resolution. The direct spectral evidence suggests that clusters with slightly long residence times in the cluster nozzle, coupled with a strong supersonic expansion, produced cold clusters. The temperature-dependent photoelectron spectra enabled ab initio molecular dynamic simulations to yield information about both the cluster structures and their temperatures. The theoretical simulations indicate that the cold clusters have temperatures between 200-300 K while the hot clusters have temperatures as high as 1000 K (J. Akola, M. Manninen, H. Haekkinen, U. Landman, X. Li, and L.S. Wang, Phys. Rev. B 60, 11297, 1999), all were obtained with a very slight change of cluster source conditions. Details of the temperature studies are focused in this contribution.