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  1. Title: Structure and interactions of ultracold Yb ions and Rb atoms

    Author(s): Lamb H.D.L., McCann J.F., McLaughlin B.M., Goold J., Wells N., Lane I.

    Physical Review A, 86, pp. 022716- (AUG 2012)

    doi: 10.1103/PhysRevA.86.022716

    In order to study ultracold charge-transfer processes in hybrid atom-ion traps, we have mapped out the potential-energy curves and molecular parameters for several low-lying states of the Rb, Yb+ system. We employ both a multireference configuration interaction and a full configuration interaction (FCI) approach. Turning points, crossing points, potential minima, and spectroscopic molecular constants are obtained for the lowest five molecular states. Long-range parameters, including the dispersion coefficients, are estimated from our ab initio data. The separated-atom ionization potentials and atomic polarizability of the ytterbium atom (αd=128.4 atomic units) are in good agreement with experiment and previous calculations. We present some dynamical calculations for (adiabatic) scattering lengths for the two lowest (Yb, Rb+) channels that were carried out in our work. However, we find that the pseudopotential approximation is rather limited in validity and only applies to nK temperatures. The adiabatic scattering lengths for both the triplet and singlet channels indicate that both are large and negative in the FCI approximation.

  2. Title: Electronic states and spin-forbidden cooling transitions of AlH and AlF

    Author(s): Wells N., Lane I.

    Physical Chemistry Chemical Physics, 13, pp. 19018- (AUG 2011)

    doi: 10.1039/c1cp21313j

    The feasibility of laser cooling AlH and AlF is investigated using ab initio quantum chemistry. All the electronic states corresponding to the ground and lowest two excited states of the Al atom are calculated using multi-reference configuration interaction (MRCI) and the large AV6Z basis set for AlH. The smaller AVQZ basis set is used to calculate the valence electronic states of AlF. Theoretical Franck–Condon factors are determined for the A1Π → X1Σ+ transitions in both radicals and found to agree with the highly diagonal factors found experimentally, suggesting computational chemistry is an effective method for screening suitable laser cooling candidates. AlH does not appear to have a transition quite as diagonal as that in SrF (which has been laser cooled) but the A1Π → X1Σ+ transition transition of AlF is a strong candidate for cooling with just a single laser, though the cooling frequency is deep in the UV. Furthermore, the a3Π → X1Σ+ transitions are also strongly diagonal and in AlF is a practical method for obtaining very low final temperatures around 3 μK.

  3. Title: Prospects for ultracold carbon via charge exchange reactions and laser cooled carbides

    Author(s): Wells N., Lane I.

    Physical Chemistry Chemical Physics, 13, pp. 19036- (2011)

    doi: 10.1039/c1cp21304k

    Strategies to produce an ultracold sample of carbon atoms are explored and assessed with the help of quantum chemistry. After a brief discussion of the experimental difficulties using conventional methods, two strategies are investigated. The first attempts to exploit charge exchange reactions between ultracold metal atoms and sympathetically cooled C+ ions. Ab initio calculations including electron correlation have been conducted on the molecular ions [LiC]+ and [BeC]+ to determine whether alkali or alkaline earth metals are a suitable buffer gas for the formation of C atoms but strong spontaneous radiative charge exchange ensure they are not ideal. The second technique involves the stimulated production of ultracold C atoms from a gas of laser cooled carbides. Calculations on LiC suggest that the alkali carbides are not suitable but the CH radical is a possible laser cooling candidate thanks to very favourable Frank-Condon factors. A scheme based on a four pulse STIRAP excitation pathway to a Feshbach resonance is outlined for the production of atomic fragments with near zero centre of mass velocity.

  4. Title: Ab initio potentials of F + Li-2 accessible at ultracold temperatures

    Author(s): Wright K.W.A., Lane I.

    Physical Review A, 82, pp. 032715- (2010)

    doi: 10.1103/PhysRevA.82.032715

    Ab initio calculations for the strongly exoergic Li2+F harpoon reaction are presented using density-functional theory, complete active space self-consistent field, and multireference configuration interaction methods to argue that this reaction would be an ideal candidate for investigation with ultracold molecules. The lowest six states are calculated with the aug-correlation-consistent polarized valence triple-zeta basis set and at least two can be accessed by a ground rovibronic Li2 molecule with zero collision energy at all reaction geometries. The large reactive cross section (characteristic of harpoon reactions) and chemiluminescent products are additional attractive features of these reactions.