Rotational rainbow scattering of oriented molecules

Molecule surface interactions depend on many degrees of freedom. In this report one degree of freedom is discussed in particular: the dependence of the interaction on the molecular orientation. Using electrostatic fields a thermal beam of oriented NO molecules is produced. By scattering this beam from a crystal, steric effects are measured for the direct scattering and adsorption of NO on Ag(111) and Pt(111). The interaction is quite different for both systems. Nevertheless, rotational rainbow scattering when the O-end of the molecule is facing the surface is observed in both cases. For NO-Pt(111) rotational rainbows are only observed at energies around 0.5 eV. Very strong randomisation is observed for NO scattering from Pt(111) at higher energies. The results are discussed in terms of the possible elementary topology of the potential energy surfaces.