Mechanism for the off-normal emission of N2 in the desorption-mediated reaction of NO on a Pd(110) surface

Desorption of NO molecules from Pd(110) at 490 K mediates the emission of N-2 and N2O, The N2 emitted at 490 K has a spatial distribution with a maximum intensity at 38 degrees from the surface normal in the [001] direction, which is expressed by 0.9 Cos4(.2) theta + 1.9 Cos(46)(theta +/- 38 degrees). In contrast, the desorptions of NO and N2O at 490 K follow a cos theta and a cos(2)theta distribution, respectively. Desorption of (NO)-N-14 from a N-15 preadsorbed Pd(110) surface mediated predominant desorption of (NN)-N-14-N-15 in the off-normal distribution, whereas the N-15(2) desorption by the recombination of N-15 atoms follows a cos(6)theta-cos(7)theta distribution. These results suggest that the reaction coordinate for the N(ad) + NO(ad) - N(2)up arrow + O(ad) reaction is responsible for the off-normal emission of N-2 On the other hand, Nz produced by a catalytic reaction of NO + H-2 at 600 K follows a cos theta distribution. On the basis of these experiments, we believe that the spatial distributions of desorbing molecules for this system are related to the reaction mechanism, especially, the orientation of the coordinate for the desorption process.