The interaction of hyperthermal nitrogen with N-covered Ag(111)

Amixed beam of hyperthermal N atoms and N2 molecules was scattered from the N-covered Ag(111) surface held at 300 K. The angular distribution of scattered N atoms is very broad. In contrast, N2 molecules exhibit a sharp angular distribution. Taking into account the relative mass ratio, N loses more energy at the surface than N2. In terms of energy loss, the atoms approximately follow the binary collision model while the molecules do not. Instead, the energy curves of scattered N2 are more comparable to the parallel momentum conservation model for near specular outgoing angles (40◦–65◦). For both atoms and molecules the angle-resolved intensity and final energy curves are very similar to those from the bare surface. However, the N-covered surface yields non-negligible N2 intensity for a broad range of outgoing angles, including along the surface normal. This was not the case from the clean surface, where the measured intensity distribution was confined to the narrower angular range indicated above. Backscattering and direct abstraction reactions are evaluated as possible origins of this additional N2 signal. Of these, an abstraction mechanism appears to be the most consistent with the measured data.