Model for nuclear spin product-state distributions of ultracold chemical reactions in magnetic fields

Based on a theoretical model where the nuclear spins remain unchanged during collision, we provide an analytical and general expression for spin state-to-state distribution of ultracold chemical reaction in magnetic field, given rotational transitions molecules. It simply requires knowledge field-dependent eigenfunctions molecular reactants products reaction. The final drastically changes with field. When is summed over all products, simplified found only required. present formalism has been successfully used to explain field behavior product-state reactions KRb molecules [Hu et al., Nat. Chem. 13, 435 (2021)].