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arXiv:1005.3471 · Physical Review A

CrRb: A molecule with large magnetic and electric dipole moments

Zoran Miroslav Pavlovic, H. R. Sadeghpour, Robin Côté, Björn Olof Roos

Published May 21, 2010• 12 citations
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Abstract

We report calculations of Born-Oppenheimer potential energy curves of the chromium-rubidium heteronuclear molecule ($^{52}\mathrm{Cr}$$^{87}\mathrm{Rb}$), and the long-range dispersion coefficient for the interaction between ground state Cr and Rb atoms. Our calculated van der Waals coefficient (${C}_{6}=1770$ a.u.) has an expected error of $3%$. The ground state ${}^{6}{\ensuremath{\Sigma}}^{+}$ molecule at its equilibrium separation has a permanent electric dipole moment of ${d}_{e}({R}_{e}=3.34\AA{})=2.90 D$. We investigate the hyperfine and dipolar collisions between trapped Cr and Rb atoms, finding elastic to inelastic cross section ratio of ${10}^{2}$--${10}^{3}$.

DOI
10.1103/physreva.81.052706

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The relativistic configuration interaction valence-bond method has been used to calculate permanent and transition electric dipole moments of the KRb heteronuclear molecule as a function of internuclear separation. The permanent dipole moment of the ground-state $X{}^{1}{\ensuremath{\Sigma}}^{+}$ potential is found to be 0.30(2) ea0{\mathrm{ea}}_{0}ea0​ at the equilibrium internuclear separation with excess negative charge on the potassium atom. For the $a{}^{3}{\ensuremath{\Sigma}}^{+}$ potential the dipole moment is an order of smaller magnitude (1 ${\mathrm{ea}}_{0}=8.47835{10}^{\ensuremath{-}30}\mathrm{Cm}).$ In addition, we calculate transition dipole moments between the two ground-state and excited-state potentials that dissociate to the K(4s)+Rb(5p)\mathrm{K}(4s)+\mathrm{Rb}(5p)K(4s)+Rb(5p) limits. Using this data we propose a way to produce singlet $X{}^{1}{\ensuremath{\Sigma}}^{+}$ KRb molecules by a two-photon Raman process starting from an ultracold mixture of doubly spin-polarized ground state K and Rb atoms. This Raman process is only allowed due to relativistic spin-orbit couplings and the absence of gerade-ungerade selection rules in heteronuclear dimers.
The properties of the electronic ground state of the polar and paramagnetic europium--S-state-atomS\text{-state-atom}S-state-atom molecules have been investigated. Ab initio techniques have been applied to compute the potential energy curves for the europium--alkali-metal-atom, EuX(X=Li,Na,K,Rb,Cs)\mathrm{Eu}X(X=\mathrm{Li},\mathrm{Na},\mathrm{K},\mathrm{Rb},\mathrm{Cs})EuX(X=Li,Na,K,Rb,Cs), europium--alkaline-earth-metal-atom, EuY(Y=Be,Mg,Ca,Sr,Ba)\mathrm{Eu}Y(Y=\mathrm{Be},\mathrm{Mg},\mathrm{Ca},\mathrm{Sr},\mathrm{Ba})EuY(Y=Be,Mg,Ca,Sr,Ba), and europium-ytterbium, EuYb, molecules in the Born-Oppenheimer approximation for the high-spin electronic ground state. The spin restricted open-shell coupled cluster method restricted to single, double, and noniterative triple excitations, RCCSD(T), was employed and the scalar relativistic effects within the small-core energy-consistent pseudopotentials were included. The permanent electric dipole moments and static electric dipole polarizabilities were computed. The leading long-range coefficients describing the dispersion interaction between atoms at large internuclear distances C6{C}_{6}C6​ are also reported. The EuK, EuRb, and EuCs molecules are examples of species possessing both large electric and magnetic dipole moments making them potentially interesting candidates for ultracold many-body quantum simulations when confined in an optical lattice in combined electric and magnetic fields.
Progress in ultracold experiments with polar molecules requires a clear understanding of their interactions and reactivity at ultralow collisional energies. Two important theoretical steps in this process are the characterization of interaction potentials between molecules and the modeling of the reactive scattering mechanism. Here, we report on the ab initio calculation of isotropic and anisotropic van der Waals interaction potentials for polar KRb and RbCs colliding with each other or with ultracold atoms. Based on these potentials and two short-range scattering parameters, we then develop a single-channel scattering model with flexible boundary conditions. Our calculations show that, at low temperatures (and in the absence of an external electric field), the reaction rates between molecules or between molecules and atoms have a resonant character as a function of the short-range parameters. We also find that both the isotropic and anisotropic van der Waals coefficients have significant contributions from dipole coupling to excited electronic states. Their values can differ dramatically from those solely obtained from the permanent dipole moment. A comparison with recently obtained reaction rates of fermionic 40 K 87 Rb shows that the experimental data cannot be explained by a model where the short-range scattering parameters are independent of the relative orbital angular momentum or partial wave.
Permanent electric dipole moments in molecules require a breaking of parity symmetry. Conventionally, this symmetry breaking relies on the presence of heteronuclear constituents. We report the observation of a permanent electric dipole moment in a homonuclear molecule in which the binding is based on asymmetric electronic excitation between the atoms. These exotic molecules consist of a ground-state rubidium (Rb) atom bound inside a second Rb atom electronically excited to a high-lying Rydberg state. Detailed calculations predict appreciable dipole moments on the order of 1 Debye, in excellent agreement with the observations.