What is wrong with the steric asymmetry in atom-molecule collisions?

The sign of the steric asymmetry S in rotationally inelastic state resolved atom-molecule collisions is questioned. Both experimental and theoretical results for collisions of Ar or He with NO (or ON) and At with OH (or HO) are discussed. Studies involve quantum state-selected crossed molecular beam experiments. In the case of NO, a striking oscillatory behavior of S as function of the rotational state after collision is observed. Full quantum mechanical scattering calculations with HIBRIDON reproduce the oscillation as far as the absolute value of S is concerned, but no consistency is obtained for the sign. On the other hand, comparable theoretical results for OH agree with experimental results for both absolute value and sign of S. The inconsistencies between experiment and the different theoretical approaches are described and possible solutions are discussed.