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NO adsorption on the oxygen-modified Mo(112)-p(2x1)-O surface has been studied by Auger electron spectroscopy(AES), low energy electron diffraction (LEED) and electron stimulated desorption ion angular distribution (ESDIAD). The Mo(112)-p(2x1)-O surface was prepared by annealing at 1400K under an oxygen pressure of 1x10-8 Torr. All LEED and ESDIAD experiments were performed at room temperature. Intensity of the ESDIAD pattern from the surface after annealing to the temperature at 600K following NO exposure below 0.5L is very weak. The ESDIAD pattern after NO exposure above 1L has four off-normal spots, which are [11-1], [-1-11], [-110] and [1-10] directions. The intensity of the spot of [11-1] direction is stronger than the other three spots. The two spots of [-110] and [1-10] direction have much the same intensity. LEED pattern changes drastically from 2x1 to 1x2 structure after 0.5L exposure of NO. With increasing exposure of NO, intensities of four spots of ESDIAD show the saturated tendency, but LEED pattern of 1x2 structure became gradually weak. Taking account of anti-symmetry of the ESDIAD pattern and an emitted angle of ion, the spot of [11-1] direction seems to originate from oxygen adsorbed at a tilted atop site on a first layer of Mo or a quasi-threefold site on the second layer. With increasing temperature, after 15L exposure of NO, the EADIAD pattern weaken suddenly around 800K. This temperature is corresponded to the desorption temperature of nitrogen. Because the ESDIAD pattern is mainly formed by O+ ions and oxygen atoms still exist on the surface from a result of AES, this change is probably due to a formation of oxide on Mo(112) surface |