AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM11
Orientation of N@sub 2@O on Pd (110) and Rh(110) at Low Temperatures

Monday, November 3, 2003, 11:40 am, Room 327

Session: Catalysis I: Adsorption and Reactions of Small Molecules at Surfaces
Presenter: H. Horino, Hokkaido University, Japan
Authors: H. Horino, Hokkaido University, Japan
I. Rzeznicka, Hokkaido University, Japan
K. Imamura, Hokkaido University, Japan
T. Matsushima, Hokkaido University, Japan
K. Takahashi, Institute for Molecular Science, Japan
E. Nakamura, Institute for Molecular Science, Japan
Correspondent: Click to Email
Catalytic N@sub 2@O decomposition on Pd(110) and Rh(110) has attracted much attention because N@sub 2@O is a major by-product in catalytic NO decomposition and also the intermediate emitting N@sub 2@ in an inclined way along the [001] direction. To understand this peculiar desorption, the orientation of adsorbed N@sub 2@O was examined at 60 K on Pd(110) and Rh(110) by near-edge X-ray absorption fine structure (NEXAFS). On Pd(110), N@sub 2@O adsorbs in a molecular form. Remarkable anisotropy was found in the X-ray incidence angle dependence of two @pi@ resonance NEXAFS peaks at 401 and 405 eV of the photon energy, i.e., with increasing shift of the x-ray incidence from the surface normal up to grazing angles, their intensities increased about 70% when the x-ray polarization was in a plane along the [001] direction, and for the polarization in a plane along the [11-0] direction, the intensities decreased about 25 %. It is derived that major N@sub 2@O is lying along the [001] direction and minor species is standing. This is consistent with DFT calculations. On Rh(110), at small exposures, only one @pi@ resonance at 401 eV was observed and its polarization dependence was very similar to that of N@sub 2@ (a), indicating dissociation of N@sub 2@O. N@sub 2@ (a) stands on the surface. At saturation, N@sub 2@O is partly standing, and lying either along the [001] or the [11-0] direction with similar populations, since with increasing shift of the x-ray incidence from the surface normal, the @pi@ resonance at 405 eV decreased only slightly when the polarization was in a plane in either the [001] or [11-0] direction. No anisotropy was found in NEXAFS peaks. The signal at 401 eV is affected by the contribution from co-adsorbed N@sub 2@ (a).