, Volume 73, Issue 4, pp 417-423

Stability patterns and ionization potentials of CrnOm clusters (n=3-50, m=0,1,2)

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Chromium and chromium oxide clusters (Cr n O m , n=3–50, m=0,1,2) were produced by a laser vaporization cluster source, and investigated by laser photoionization spectroscopy and photofragmentation spectroscopy in combination with mass spectrometry. Ionization potentials for Cr n O m clusters (m=1,2) deduced from photoionization spectroscopy measurements show a smoothly decreasing trend with size similar to the behavior of other transition metals. Superimposed on this is a diffuse step from 8 to 11 chromium atoms, possibly indicating a structural transition. Mass-abundance spectra recorded with low-fluence, high-photon-energy ionization (6.4 eV) reveal stability steps for Cr n O m clusters (n=3–50, m=1,2), corresponding to icosahedral geometrical shell closings insensitive to the oxygen content. These magic numbers are also found for Cr n O m + clusters (n=3–50, m=0,1,2) investigated with photofragmentation.

Received: 25 July 2001 / Revised version: 21 August 2001 / Published online: 10 October 2001