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 effect of a deep chemisorption well on the scattering dynamics we have performed measurements of rotational (J) excitation of NO in collisions with Pt(111). The measurements show surprisingly large rotational excitation and a clear rotational rainbow. Classical trajectory calculations 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 calculations with this potential explain the expermental observations qualitatively. We suggest that the rotational excitation manifested in the rotational rainbow is a result of the anistropy in the repulsive part of the interaction potential.