Beyond Born-Oppenheimer Approximation In Ultracold Atomic Collisions

We report on deviations beyond the Born-Oppenheimer approximation in potassium interatomic potentials. Identifying three previously unknown d-wave Feshbach resonances, we significantly improve the understanding of the K-39 interatomic potentials. Combining these observations with the most recent data on known inter- and intraisotope Feshbach resonances, we show that Born-Oppenheimer corrections can be determined from atomic collisional properties alone and that significant differences between the homo- and heteronuclear cases appear.