Photoemission and XAS studies of solid oxygen and alkali metal systems.
Item
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Title
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Photoemission and XAS studies of solid oxygen and alkali metal systems.
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Identifier
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AAI9207057
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identifier
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9207057
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Creator
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Chen, Jie.
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Contributor
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Chairman: Marten L. den Boer
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Date
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1991
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Condensed Matter
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Abstract
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Solid oxygen and its interaction with alkali metals have been studied using x-ray absorption spectroscopy (XAS) and photoelectron spectroscopy (PES). The Oxygen K-edge NEXAFS spectrum of solid oxygen shows three main features, and they are assigned to the {dollar}\pi\sp*{dollar}, {dollar}\sigma\sp*{dollar} resonance, and Rydberg transitions, respectively. This assignment is supported by the theoretical calculation and high resolution NEXAFS measurements. Compared with the gas phase spectrum, the Rydberg states shift about 1.5 eV to a higher photon energy, which is due to the increase of dielectric constant in the solid. The Auger spectra of both the ionized and excited molecules in solid O{dollar}\sb2{dollar} shift to a higher kinetic energy relative to the gas phase spectra. The shifts are 10 and 2 eV, respectively. These shifts are explained in terms of solid state final state screening effects. PES studies of the interaction between solid oxygen and alkali metals show that three different oxidation states can coexist at 35 K. Assignments of these features in both the O 1s core level and valence band spectra have been made for O{dollar}\sbsp{lcub}2{rcub}{lcub}-{rcub}{dollar}, O{dollar}\sbsp{lcub}2{rcub}{lcub}2-{rcub}{dollar} and O{dollar}\sp{lcub}2-{rcub}{dollar} species, which correspond to the formation of superoxide, peroxide, and oxide, respectively. The Cs 3d and the O 1s cross-section ratio obtained from experimental spectra and this assignment quantitatively agrees with the theoretical value.;We also studied LiO{dollar}\sb2{dollar}, KO{dollar}\sb2{dollar}, and CsO{dollar}\sb2{dollar} superoxides using NEXAFS and EXAFS measurements. Compared with the solid O{dollar}\sb2{dollar} NEXAFS spectrum, both the {dollar}\pi\sp*{dollar} and {dollar}\sigma\sp*{dollar} resonances in the NEXAFS spectra of all three alkali metal superoxides shift to a lower photon energy due to the transfer of electron to the molecular oxygen. The intensity ratio of these two peaks changes from about 2:1 in solid O{dollar}\sb2{dollar} to a smaller value in the superoxides because of increased occupancy of the {dollar}\pi\sp\*{dollar} level. The O-O bond length in superoxide deduced from the position of {dollar}\sigma\sp*{dollar} resonance, agrees well with the previous reported O-O distance in NaO{dollar}\sb2{dollar} and KO{dollar}\sb2{dollar}. Both the O-O and O-Cs distances obtained from the EXAFS study on cesium superoxide (CsO{dollar}\sb2{dollar}) are in good agreement with previous x-ray diffraction measurements on NaO{dollar}\sb2{dollar} and KO{dollar}\sb2{dollar}.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
