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We compare and contrast the wide Feshbach resonances and the corresponding weakly bound states in the lowest scattering channels of ultracold 6Li and 7Li. We use high-precision measurements of binding energies and scattering properties to determine interaction potentials that incorporate non-Born-Oppenheimer terms to account for the failure of mass scaling between 6Li and 7Li. Correction terms are needed for both the singlet and the triplet potential curves. The universal formula relating binding energy to scattering length is not accurate for either system. The 6Li resonance is open-channel-dominated and the van der Waals formula of Gao [J. Phys. B 37, 4273 (2004)] gives accurate results for the binding energies across much of the resonance width. The 7Li resonance, by contrast, is weakly closed-channel-dominated and a coupled-channel treatment of the binding energies is required. Plotting the binding energies in universal van der Waals form helps illustrate subtle differences between the experimental results and different theoretical forms near the resonance pole. [ABSTRACT FROM AUTHOR]

We have investigated magnetically tunable Feshbach resonances arising from the interaction of Li(²S) with metastable Yb(³P2) and (³P0). For Yb(³P2), all the resonance features are strongly suppressed by inelastic collisions that produce Yb in its lower-lying ³P1 and ³P0 states. For Yb(³P0), sharp resonances exist but they are extremely narrow (widths less than 1 mG). [ABSTRACT FROM AUTHOR]

We explore the feasibility of producing ultracold diatomic molecules with nonzero electric and magnetic dipole moments by magnetically associating two atoms, one with zero electron spin and one with nonzero spin. Feshbach resonances arise through the dependence of the hyperfine coupling on internuclear distance. We survey the Feshbach resonances in diatomic systems combining the nine stable alkali-metal isotopes with those of Yb, focusing on the illustrative examples of RbYb and CsYb. We show that the resonance widths may expressed as a product of physically comprehensible terms in the framework of Fermi's golden rule. The resonance widths depend strongly on the background scattering length, which may be adjusted by selecting the Yb isotope, and on the hyperfine coupling constant and the magnetic field. In favorable cases the resonances may be over 100 mG wide. [ABSTRACT FROM AUTHOR]

We investigate the effect of hyperfine interactions on ultracold molecular collisions in magnetic fields, using 24Mg(¹S)+ 14NH(³Σ-) as a prototype system. We explore the energy and magnetic-field dependence of the cross sections, comparing the results with previous calculations that neglected hyperfine interactions [A.O.G. Wallis and J. M. Hutson, Phys. Rev. Lett. 103, 183201 (2009)]. The main effect of hyperfine interactions for spin relaxation cross sections is that the kinetic energy release of the dominant outgoing channels does not reduce to zero at low fields. This results in reduced centrifugal suppression of the cross sections and increased inelastic cross sections at low energy and low field. We also analyze state-to-state cross sections, for various initial states, and show that hyperfine interactions introduce additional mechanisms for spin relaxation. In particular, there are hyperfine-mediated collisions to outgoing channels that are not centrifugally suppressed. However, for Mg + NH these unsuppressed channels make only small contributions to the total cross sections. We consider the implications of our results for sympathetic cooling of NH by Mg and conclude that the ratio of elastic to inelastic cross sections remains high enough for sympathetic cooling to proceed. [ABSTRACT FROM AUTHOR]

Semiempirical potential energy surfaces for Br–HBr are constructed, based on empirical Kr–HBr, Kr–Br and Kr–Kr potentials. The electrostatic forces due to the interaction of the quadrupole of the Br atom with the multipoles of the HBr molecule are included, and make a substantial contribution to the well depths. The potentials are presented in diabatic and adiabatic representations, with and without spin–orbit coupling. When spin–orbit coupling is included, the adiabatic well depth is 342 cm^-1, at a linear Br–H–Br configuration. Fully coupled bound-state calculations are carried out, and the ground state is found to be bound by 269 cm^-1. If the complex can be observed spectroscopically, it will provide a sensitive probe of the potential energy surfaces in the entrance and exit valleys of the Br+HBr reaction. In addition, the complex is likely to be important as a product of photodissociation of HBr in HBr dimer.

We obtain the interaction potential for NaCs by fitting to experiments on ultracold scattering and spectroscopy in optical tweezers. The central region of the potential has been accurately determined from Fourier transform spectroscopy at higher temperatures, so we focus on adjusting the long-range and short-range parts. We use coupled-channel calculations of binding energies and wave functions to understand the nature of the molecular states observed in ultracold spectroscopy and of the state that causes the Feshbach resonance used to create ultracold NaCs molecules. We elucidate the relationships between the experimental quantities and features of the interaction potential. We establish the combinations of experimental quantities that determine particular features of the potential. We find that the long-range dispersion coefficient C6must be increased by about 0.9% to 3256(1)Eha06to fit the experimental results. We use coupled-channel calculations on the final potential to predict bound-state energies and resonance positions.