STERIC ASYMMETRY IN ROTATIONALLY INELASTIC STATE-RESOLVED NO-AR COLLISIONS

The first direct experimental evidence is reported of large orientatio n (head-tail) effects in rotationally inelastic collisions, for the sp ecific case of NO and Ar. NO is selected in the (2) Pi(1/2) j = 1/2(-) state and oriented in an electric field. The steric effect, measured for collisions to three distinct final rotational states, appears to d epend on the j ' value and the parity of the final state. This behavio ur also follows from quantum-mechanical scattering calculations, but t he calculated values do not coincide with the corresponding experiment al ones.