Photoelectron spectroscopic studies covalency

Didziulis, S. V., S. L. Cohen, K. D. Butcher, and E. I. Solomon (1988). Variable photon energy photoelectron spectroscopic studies of covalent bonding in Sd " transition-metal compounds. Inorg. Chem. 27, 2238-50. 

While many spectroscopic studies have been published on dimers, the most extensive polymer studies have been with Ag, Na, and Cu clusters. As might be expected much of the interest in silver relates to the photographic process where it appears that a four-atom silver cluster on a silver halide surface leads to reduction by developer, whereas a three-atom cluster does not. The electron spin resonance (ESR) spectrum of sodium in argon confirms that the trimer is covalently bonded and not an equilateral triangle. Ultraviolet photoelectron spectroscopy (UPS) of Cu clusters indicates that the d band is separate from the s band, unlike in the bulk or in the Xa calculations mentioned earlier. 

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