Electronic Supplementary Material

Characterization of Cerium and Oxygen Atoms in Free Clusters of Cerium Oxide
by X-ray Absorption Spectroscopy

Tetsuichiro Hayakawa1#, Masashi Arakawa2, Shun Sarugaku2, Kota Ando2, Kenichirou Tobita2, Yuya Kiyomura2, Tomoki Kawano2, Akira Terasaki1,2,#

1 East Tokyo Laboratory, Genesis Research Institute, Inc., 717-86 Futamata, Ichikawa, Chiba 272-0001, Japan

2 Department of Chemistry, Faculty of Science, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan

Fragment-ion yield and bonding character of unoccupied states

The peaks in the X-ray absorption spectra near the O K-edge region originate from excitation of 1s electrons of the O atoms into unoccupied states. Bonding character of the unoccupied states can be discussed from fragment-ion distribution because the fragmentation pathway is dependent on the excited state after X-ray absorption [1]. The panels (A1)−(D1) of Fig. S1 show O K-edge spectra of partial yields of fragment ions, i.e., Ce2+, Ce+, CeO+ and CeO2+, produced from Ce3O4−7+ along with the total fragment-ion yield, I(total). Ce+ and CeO+ are observed as dominant species among fragment ions. The panels (A2)−(D2) show branching fractions of these two dominant species, I(Ce+) / I(total) and I(CeO+) / I(total). In the main peak and peak A region, the fraction of Ce+ decreases, whereas that of CeO+ increases. This result suggests that the charge initially created on an O atom tends not to be redistributed to surrounding Ce atoms. Because the charge redistribution is a process competing with cluster dissociation, it is speculated that electron excitation would take place into anti-bonding molecular orbital; this excitation weakens the bond in the cluster to promote dissociation before charge redistribution, and thus the branching to molecular CeO+ is preferred.

Fig. S1 Branching of Ce3O4−7+ fragmentation at O K-edge. (A1−D1): total and partial yields of fragment ions; (A2−D2): branching fractions of Ce+ and CeO+. The solid curves show eye guides

Reference

1.  Hayakawa T, Egashira K, Arakawa M, Ito T, Sarugaku S, Ando K, Terasaki A (2016) X-ray absorption spectroscopy of Ce2O3+ and Ce2O5+ near Ce M-edge. J Phys B: At Mol Opt Phys 49: 075101

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