Stability patterns and ionization potentials of CrnOm clusters (n=3-50, m=0,1,2)
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Chromium and chromium oxide clusters (CrnOm, 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 CrnOm 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 CrnOm 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 CrnOm+ clusters (n=3–50, m=0,1,2) investigated with photofragmentation.
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