Charge transfer in cold Yb++Rb collisions

Abstract

Charge-transfer cold Yb + + Rb collision dynamics is investigated theoretically using high-level ab initio potential energy curves, dipole moment functions and nonadiabatic coupling matrix elements. Within the scalar-relativistic approximation, the radiative transitions from the entrance A 1 Σ + to the ground X 1 Σ + state are found to be the only efficient charge-transfer pathway. The spin-orbit coupling does not open other efficient pathways, but alters the potential energy curves and the transition dipole moment for the A − X pair of states. The radiative, as well as the nonradiative, charge-transfer cross sections calculated within the 10 −3 − 10 cm −1 collision energy range exhibit all features of the Langevin ion-atom collision regime, including a rich structure associated with centrifugal barrier tunneling (orbiting) resonances. Theoretical rate coefficients for two Yb isotopes agree well with those measured by immersing Yb + ion in an ultracold Rb ensemble in a hybrid trap. Possible origins of discrepancy in the product distributions and relations to previously studied similar processes are discussed.

Formation of molecular ions by radiative association of cold trapped atoms and ions

“…This discrepancy of 113 cm −1 also holds for the spacing between the Yb + ( s 6 )+(Alk)(ns) and the Yb( s S 6 2 1 )+(Alk) + asymptotes (equal to 16864.8 cm −1 in our method, in good agreement with the experimental value of 16752.2 cm −1 [64]). It favorably compares to the discrepancy of 322 cm −1 reported in [66], and to [67] which reported an energy difference of 16279 cm −1 between these two asymptotes. Finally, in their work on LiYb + [13] the authors report an ionization energy for the Yb ground state of 50267 cm −1 .…”

“…As already quoted above, the cases of RbYb + and LiYb + are peculiar, as the Yb + ion and Yb atom have not been treated with a large ECP before. Tables 1 and 2 reveal a contrasted situation for RbYb + in comparison with the results of [66,67,74] that are all obtained with similar approaches based on small core ECPs. Our values for R e and D e of the X PEC are in good agreement with those of [67], while the potential well depth from [66,74] is twice smaller than ours, with a minimum located at a significantly larger distance.…”

“…The RA process is even more favored in RbBa + due to the double well in the A potential curve, which enhances the spontaneous emission towards X bound levels around the top of the barrier where the TEDM is large. In all cases, the shape resonances in the RA and RCT cross sections are the same, as they are due to the centrifugal barrier in the entrance channel (see also [67,73]). In the framework of the present model, the choice of the isotopologues for each ionic species does not yield significantly different cross sections in magnitude, as the reduced mass (which differs by less than one percent among a series of isotopologues of a given ion) is involved only through the kinetics described by the radial wave functions.…”

Non-radiative inelastic processes in lithium-helium ion-atom collisions

“…A general conclusion from this controversial behavior would be that radiative processes are expected to be dominant over non-radiative ones at low energies. This finding actually agrees with the results of the treatment of radiative and non-radiative processes in He + + H collisions (Zygelman et al 1989), as well as in cold and ultra-cold Yb + + Rb collisions (Sayfutyarova et al 2013).…”

Charge-exchange collisions between ultracold fermionic lithium atoms and calcium ions

“…Similar results have been reported for experimental trials using the Rb-Yb + system, in which the reaction rates of ions in the metastable D 3/2 and F 7/2 states were investigated in detail [7]. Energy level crossing may thus occur in the Li + +Ca (3d4s 3 D) level and Li + Ca + (D 3/2 or D 5/2 ) levels at sufficiently short distances at which the interaction potentials may be modified when working at high energy levels [16,21]. A quantitative understanding of the charge exchange collision coefficients determined for our system will require further studies of the related energy levels.…”