Photoelectron spectroscopy of size‐selected transition metal clusters: Fen, n=3–24

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摘要：

A higher resolution magnetic bottle photoelectron spectrometer for the study of the electronic structure of size‐selected metal clusters is presented. The initial study on Fen(n=3–24) is reported at a photon energy of 3.49 eV. The photoelectron spectra of these clusters exhibit sharp features throughout the size range. The spectra for Fe3–8show large size dependence with many resolved features. The spectra for Fe9–15exhibit some similarity with each other, all with a rather sharp feature near the threshold. An abrupt spectral change occurs at Fe16, then again at Fe19and Fe23. These photoelectron spectral changes coincide remarkably with changes of the cluster reactivity with H2. Extended Hückel molecular orbital (EHMO) calculations are performed for all the clusters to aid the spectral interpretations. The calculations yield surprisingly good agreement with the experiment for clusters beyond Fe9when body‐centered cubic (bcc) structures are assumed for Fe9–15and a similarly close‐packed structure with a bcc Fe15core for the larger clusters. The EHMO calculations allow a systematic interpretation of the sharp photoelectron spectral features in Fe9–15and reproduced the abrupt spectral change taking place from Fe15to Fe16. Most importantly, the reactivity changes of the clusters with H2are successfully explained based on the detailed electronic structures of the clusters, as revealed from the photoelectron spectroscopy (PES) spectra and the theoretical calculations. The calculations also correctly predict the existence of magnetism in these clusters and yield reasonable values for the cluster magnetic moments.

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关键词：

Experimental/ atomic clusters EHT calculations iron magnetic moments metal clusters negative ions photoelectron spectra time of flight spectra/ magnetic bottle photoelectron spectrometer photoelectron spectroscopy size-selected transition metal clusters Fe n- electronic structure photon energy spectral change extended Huckel molecular orbital calculations spectral interpretation body-centered cubic structures Fe 9 Fe 19- Fe 16- cluster reactivity magnetism cluster magnetic moments modified Wilky-McLaren time of flight mass spectrometer Fe 3 Fe 4 Fe 5 Fe 6 Fe 7 Fe 8 Fe 10 Fe 11 Fe 12 Fe 13 Fe 14 Fe 15 Fe 16 Fe 17 Fe 18 Fe 19 Fe 20 Fe 21 Fe 22 Fe 23 Fe 24/ A3365 Photoelectron spectra of molecules A3640 Atomic and molecular clusters A3120P Other semi-empirical calculations (atoms and molecules) A3580 Atomic and molecular measurements and techniques/ Fe3/el Fe /el Fe4/el Fe /el Fe5/el Fe /el Fe6/el Fe /el Fe7/el Fe /el Fe8/el Fe /el Fe9/el Fe /el Fe10/el Fe /e