ROTATIONAL RAINBOWS IN NO SCATTERING FROM PT(111)

The interaction between NO and Pt(111) is dominated by the presence of a deep well corresponding to molecular chemisorption. To study the ef fect of a deep chemisorption well on the scattering dynamics we have p erformed measurements of rotational (J) excitation of NO in collisions with Pt(111). The measurements show surprisingly large rotational exc itation and a clear rotational rainbow. Classical trajectory calculati ons were carried out to examine the origin of this rainbow. Using the potential of Haug et al. the observed energy dependence of the rainbow could not be reproduced. We have constructed another model potential, having a shallow well for the O end of the molecule. Trajectory calcu lations with this potential explain the experimental observations qual itatively. We suggest that the rotational excitation manifested in the rotational rainbow is a result of the anisotropy in the repulsive par t of the interaction potential.