Charge Exchange Dynamics in Cold Collisions of ${}^{40}$CaH${}^{+}$ and ${}^{39}$K

Abstract

We report the observation of charge-exchange collisions between trapped calcium monohydride molecular ions (${}^{40}$CaH${}^{+}$) and ultracold potassium atoms (${}^{39}$K) in a hybrid ion-atom trap. The measured charge-exchange rate coefficient is significantly suppressed relative to the Langevin rate constant for the system. We use $abinitio$ quantum-chemical calculations to model the (CaH-K)${}^{+}$ complex in the ground and excited electronic states and to identify possible charge-exchange mechanisms. Our calculations rule out a direct non-radiative charge-exchange reaction and instead point to a radiative mechanism, but do not quantitatively reproduce the measured rate, highlighting the need for a full-dimensional quantum dynamics treatment that includes vibrational motion and intermediate complex formation. Our work demonstrates that cold hybrid ion-atom platforms with molecular ions enable access to richer chemical complexity and collisional dynamics inaccessible in purely atomic systems.

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