State-resolved diffraction oscillations imaged for inelastic collisions of NO radicals with He, Ne and Ar.

Just as light scattering from an object results in diffraction patterns, the quantum mechanical nature of molecules can lead to the diffraction of matter waves during molecular collisions. This behaviour manifests itself as rapid oscillatory structures in measured differential cross-sections, and such observable features are sensitive probes of molecular interaction potentials. However, these structures have proved challenging to resolve experimentally. Here, we use a Stark decelerator to form a beam of state-selected and velocity-controlled NO radicals and measure state-to-state differential cross-sections for inelastic collisions of NO with He, Ne and Ar atoms using velocity map imaging. The monochromatic velocity distribution of the NO beam produced scattering images with unprecedented sharpness and angular resolution, thereby fully resolving quantum diffraction oscillations. We found excellent agreement with quantum close-coupling scattering calculations for these benchmark systems.