State resolved investigation of F\"orster resonant energy transfer in collisions between polar molecules and Rydberg atoms

Investigation of collisions between molecules and Rydberg atoms provides access to a wide range of interesting processes, including, e.g., molecule-ion collisions, ionization, and electron capture. A particular fascinating aspect results from coincidences between the energy spacing of molecular rotational states and Rydberg states, leading to F\"orster resonant energy transfer between the two systems.\\ Combining state selective field ionization of Rydberg atoms with millimeter-wave state transfer allows us to perform fully state resolved measurements of Rydberg-atom populations. This allows us to investigate energy transfer between ammonia molecules and rubidium Rydberg atoms in detail~[1]. Varying the Rydberg atom transition frequency by changing the initial Rydberg state and tuning the transition with electric fields allows us to investigate the depence of the resonant energy transfer on the resonance condition. Examining the populations of different Rydberg angular momentum states including different M-sublevels allows us to study angular momentum selection rules for the molecule-Rydberg-atom interactions.\\ \noindent[1] F. Jarisch {\it et al.} NJP {\bf 20}, 113044 (2018)