Angular and velocity distributions of HD molecules produced by the H2–D2 exchange reaction on the stepped Pt(557) surface

The H2–D2 exchange reaction on Pt(557) crystal surface was investigated using a molecular beam surface scattering technique. The angular and velocity distributions of the HD product were measured at various crystal temperatures (500–1170 K). It was found that the exchange reaction occurred via interactions of adsorbed H and D atoms (Langmuir–Hinshelwood mechanism). Although the HD that is produced desorbs with a cos2 θ angular distribution, its translational energy corresponds to a temperature slightly colder than that of the substrate with the mean energy of the desorbing molecules depending on the desorption angle. As the desorbing angle increases away from the surface normal, the mean translational energy decreases. The exchange reactivity was found to be incident azimuthal angle dependent while the translational energy of the product HD is independent of the azimuthal angle of detection.