Hyperfine structure of the hydroxyl free radical (OH) in electric and magnetic fields

Abstract

We investigate single-particle energy spectra of the hydroxyl free radical (OH) in the lowest electronic and rovibrational level under combined static electric and magnetic fields, as an example of heteronuclear polar diatomic molecules. In addition to the fine-structure interactions, the hyperfine interactions and centrifugal distortion effects are taken into account to yield the zero-field spectrum of the lowest Π 2 3 2 manifold to an accuracy of less than 2 kHz. We also examine level crossings and repulsions in the hyperfine structure induced by applied electric and magnetic fields. Compared to previous work, we found more than 10% reduction of the magnetic fields at level repulsions in the Zeeman spectrum subjected to a perpendicular electric field. In addition, we find new level repulsions, which we call Stark-induced hyperfine level repulsions, that require both an electric field and hyperfine structure. It is important to take into account hyperfine structure when we investigate physics of OH molecules at micro-Kelvin temperatures and below. 2 3 2 manifold to an accuracy of less than ∼ 2 kHz 100 nK. As OH nears the quantum degenerate regime, producing a sample in a single quantum state will require manipulation OPEN ACCESS RECEIVED of the hyperfine degrees of freedom, as was the case for ultracold KRb molecules [18]. Our results are essential for achieving this high degree of control over hyperfine states with the required spectroscopic precision. We also examine level crossings and repulsions in hyperfine structure in the presence of applied electric and magnetic fields to explore how these level crossings and repulsions change when we change the relative angle between the electric and magnetic fields. It has never been performed before us to couple the 16 states in the lowest Π 2 3 2 manifold with the 80 excited states in the presence of strong fields and obtain such accuracies comparable with ultracold temperatures. Ahead of ultracold molecules, ultracold gases of atoms with magnetic dipole moments, or atomic dipolar gases, have been intensely investigated. Gases of chromium [19], dysprosium [20], and erbium [21] have been trapped and cooled down to quantum degeneracy in experiments. Due to their anisotropic long-range dipoledipole interactions, atomic dipolar gases are expected to exhibit novel quantum phenomena: spin textures [22-24], dipolar relaxation [25], Einstein-de Haas effects [26,27] in their bosonic spieces, and ferronematic [28,29] and antiferrosmectic-C phases [30] in their fermionic species. However, dipole-dipole interactions between atoms are fixed in strength by their permanent magnetic dipole moments. In contrast, polar molecules offer an electric dipole moment that is directly tunable via an applied electric field and can be made orders of magnitude larger than dipole moments in atoms. Cold and ultracold gases of molecules with electric dipole momentsmolecular dipolar gases-are at or rapidly approaching quantum degeneracy in experiments, e.g., KRb [31], RbCs [32], RbSr [33], OH [8], a...

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