Imaging diffraction oscillations for inelastic collisions of NO radicals with He and D₂

We present state-to-state differential cross sections for collisions of NO molecules (X²Π_1/2,j=1/2,f) with He atoms and ortho-D₂ (j = 0) molecules as a function of collision energy. A high angular resolution obtained using the combination of Stark deceleration and velocity map imaging allows for the observation of diffraction oscillations in the angular scattering distributions. Differences in the differential cross sections and, in particular, differences in the angular spacing between individual diffraction peaks are observed. Since the masses of D₂ and He are almost equal and since D₂(j = 0) may be considered as a pseudo-atom, these differences directly reflect the larger size of D₂ as compared to He. The observations are in excellent agreement with the cross sections obtained from quantum close-coupling scattering calculations based on accurate ab initio NO-He and NO-D₂ potential energy surfaces. For the latter, we calculated a new NO-D₂ potential energy surface.