Mixed-field effect at the hyperfine level of ¹²⁷I⁷⁹Br in its rovibronic ground state: Toward field manipulation of cold molecules

The mixed-field effect at the hyperfine level of the rovibronic ground state of the ¹²⁷I⁷⁹Br (X¹Σ, v = 0, J = 0) molecule is computed on the J–I uncoupled basis of |JM_JI₁M₁I₂M₂〉, where J is the molecular total angular momentum excluding nuclear spin, M_J is the projection number of J, I₁ and I₂ are the nuclear spins of the iodine and bromine atoms, and M₁ and M₂ are the projection numbers of I₁ and I₂, respectively. When the two applied electric and magnetic fields are parallel, the perturbations are rare and only one perturbation is observed in a relatively large field regime in our computation range. However, when the two fields are off-parallel, the perturbations increase significantly and some sublevels show the Feshbach-like resonance phenomenon. Therefore, such sublevels transit between weak-field seeking and strong-field seeking repeatedly, which can be utilized to enhance or suppress cold molecular collision and chemical reaction rates. Such behavior of the molecular hyperfine structure in the mixed off-parallel fields may also be utilized to construct an electric-field-assisted anti-Helmholtz magnetic trap for cold molecules and to realize evaporative cooling of cold molecules (sub-mK) into the ultracold regime (μK).