Quantum phenomena that lead to the formation of long-lived collision complexes, such as scattering resonances, play a central role in the outcome of cold collisions. These resonances are fundamental probes of the fine details of internuclear interactions and are used to associate cold molecules from laser-cooled atoms. Here we present a new method to populate and probe near-threshold Feshbach resonance states. We demonstrate our ability to filter out the resonance pathway from complex collision processes involving reactive, inelastic, and elastic pathways. Our method is based on the coincidence detection of electron/ion momenta in Penning ionization collisions between metastable noble gas atoms and neutral molecules. Here, in a single measurement, we measure both the resonance energy and the final state distribution with quantum state-to-state resolution. We obtain several tens of quantum numbers per measurement without any laser detection schemes. Although we study resonance states in a strongly interacting and highly anisotropic molecular ion-neutral atom collision system, we are able to observe a unique quantum signature of the resonance states on the final state distribution. In addition, we present an experimental scheme for control of the final state distribution, which is based on the initial constraint of total angular momentum at the ionization step of the dynamics. The latter is motivated by our recent observation of a partial wave resonance at the lowest state of relative angular momentum.
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