OPTICAL SPECTROSCOPY OF METAL-CLUSTERS - CU-4(+)

The absorption spectrum of Cu4 + has been recorded in the visible region of the spectrum (710-370 nm) by monitoring the photodissociation of Cu4 + to give Cu3 +. Ten electronic transitions have been identified, and most of them show vibrational fine structure. The transitions appear to fall into two groups. A group centered around 650 nm has been tentatively assigned to mainly d → s type transitions. This group of transitions can be correlated with an interband transition of bulk copper, suggesting that the incipient band structure of the bulk is apparent even in a cluster containing as few as four atoms. The vibronic structure of the band systems at 600, 690, and 565 nm is discussed in detail and some plausible assignments are proposed. © 1990.