Peculiar nitrogen desorption on rhodium surfaces and the decomposition mechanism of nitrogen oxides

冷却性能和泵浦速率的提高角分辨热解吸仪中的样品晶体被成功地从90K冷却到50K。N2O在干净的Rh(110)上分解，在60K已经分解，在70-170K范围内产生5个N_2脱附峰，在165K左右达到峰值的β_1-N_2呈余弦分布，表明N_2O解离后从表面捕获的N_2脱附一次。Β_2-N_2在140K达到峰值，β_3-N_2在120K达到峰值。这些峰出现在较高的N_2O曝光量下，并与平面上的表面法线成68度角的[001]方向准直。另一方面，在少量N_2O暴露下，观察到β_4-N_2和β_5-N_2。N_2的脱附对表面剩余氧的量很敏感。通过选择预热温度来控制N_2O的量，当预热温度低于1000K时，N_2O不分解，在1100K预热后，N_2O在100-170K分解，释放出沿[001]方向30度左右准直的N_2。LEED观察到一种(1x2)缺行结构。用近边X射线吸收精细结构研究了70 K时Rh(110)表面吸附N_2O的取向。在低N_2O暴露下，N_2O在70K时部分解离。在较高的N_2O覆盖率下，存在站立和躺着两种吸附形式，在Pd(110)上对N_2O的分解和吸附也得到了类似的结果。

Improvements of cooling performance and pumping rates ; A sample crystal in the angle-resolved thermal desorption apparatus was successfully improved to be cooled from 90K to 50K. The pumping rate was increased about 5 times and high enough to reduce the background signal level to one fifth.N_2O decomposition on clean Rh(110) ; N_2O is already decomposed from 60 K and yields five N_2 desorption peaks in the range of 70-170 K. β_1-N_2 peaking at around 165 K shows a cosine distribution, indicating desorption from N_2 trapped once on the surface after N_2O dissociation. Β_2-N_2 peaked at 140 K and β_ 3-N_2 at 120K. These peaks appeared at higher N_2O exposures and collimate at 68 degrees from the surface normal in the plane in the [001] direction. On the other hand, both β_4-N_2 and β_5-N_2 were observed at small N_2O exposures. These collimate 68 degrees off the surface normal into the [001] direction.N_2 desorption is sensitive to the amount of residual surface oxygen. The amount was controlled by selecting pre-heating temperature, N_2O is not decomposed when the pre-heating is below 1000 K. After the pre-heating at 1100 K, N_2O is decomposed at 100-170 K, emitting N_2 collimated at around 30 degrees along the [001] direction. A (1x2) missing-row structure was observed by LEED. The 30 degree component was proposed to be formed on declining terraces on the missing-row structure.The orientation of adsorbed N_2O on Rh(110) was examined at 70 K by near-edge X-ray absorption fine structure. N_2O is partly dissociated at 70 K at low N_2O exposures. At higher N_2O coverage, two adsorption forms, standing and lying, were proposed.Similar results were obtained on Pd(110) for N_2O decomposition and adsorption.