Liu, Yan

OH vertical column abundances have been measured since 1977. Based on this long-term data base, the terrestrial OH abundance trends, such as the high-sun (secX = 1) enhancement of the zenith angle dependence, seasonal variations, and diurnal behaviors, have been observed. Current atmospheric models do not predict these features. In this thesis, a one dimensional photochemical model of the mesosphere has been constructed in order to examine the possibility that these observed effects might originate in this region of the atmosphere. Transport effects are not considered. The model result demonstrates that the observed OH behaviors are not caused by known photochemical reactions in the mesosphere.

The electronic structures of beta'-AgMg and Ag3Mg alloys have been investigated by a combination of photoelectron spectroscopy and first-principles band structure and photocurrent calculations. The study includes the first ever XPS and UPS measurements from the ordered and disordered phases of Ag3Mg. We concentrated mainly on measurements of the valence bands and the core level binding energies for these alloys and their parent metals. The band structures of the ordered alloys and pure metals have been calculated by the SCF-LMTO-ASA method, and the KKR and KKRCPA calculational schemes have been used in order to determine the electronic structures of both ordered and disordered phases of Ag3Mg on an equal footing. For the purpose of interpreting the core level shifts due to alloying, a modified LMTO scheme has been applied, in a supercell geometry, to allow for relaxation effects. In addition, we have shown that the Fermi surface topology may well be an important factor in determining the relative stability of the long period superlattice structure in Ag3Mg. In general, the calculations are in very good agreement with the experimental results. We conclude that the combination of theoretical calculations and photoemission measurements provides a detailed understanding of the electronic structures and the properties of Ag-Mg alloys.