Observation and characterization of direct inelastic and trapping-desorption channels in the scattering of N2 from Cu(110)

Resonantly enhanced multiphoton ionization (REMPI) and time resolved molecular beam techniques were used to study the rotational state and velocity distributions of N2 scattered from Cu(110). At a surface temperature of 85 K, two peaks were observed in time-of-flight (TOF) measurements. We interpret these as a direct inelastic channel at early time and a trapping desorption channel at later time. As the surface temperature is raised the direct inelastic scattering becomes stronger as the trapping desorption channel grows weaker. Rotational state distributions show that the early TOF peak has a large number of populated states characteristic of direct inelastic scattering; the later TOF peak has a rotational state distribution well characterized by the surface temperature. The rotational state distributions of the direct-inelastic channel were found to depend linearly on both surface temperature, Ts and incident energy, Ei. The absence of rotational rainbows at low Ei and low Ts is attributed to multiple collisions with the surface.