Abstract We study the isotopic dependence of collisional widths and shifts of the Hg clock transition 1S0-3P0 perturbed by the Rbatoms in the temperature range from 1 nK to 1 K. For this purpose, we model the Born-Oppenheimer effective interactionpotential by including the leading long-range van der Waals coefficients.For elastic collisions, we show the connection betweenthe dependence of collision line shape parameters on the reduced mass of colliding partners as well as the variation of thescattering length in the excited and ground states of the Hg-Rb system in the μK temperature range. We confront the fullquantum scattering calculations with a semi-classical approximation for collisional widths and shifts. We show that the shaperesonances in excited and ground scattering states lead to significant variations of collisional line shape parameters with thechange of the reduced mass of colliding atoms. We also indicate the possible influence of inelastic collisions, which could leadto universal behavior and significantly affect the dependence of collisional broadening and shifting on the isotopic combinationof colliding atoms.
The properties of bosonic ytterbium photoassociation spectra near the intercombination transition ${^{1}S}_{0}\ensuremath{-}{^{3}P}_{1}$ are studied theoretically at ultralow temperatures. We demonstrate how the shapes and intensities of rotational components of optical Feshbach resonances are affected by mass tuning of the scattering properties of the two colliding ground-state atoms. Particular attention is given to the relationship between the magnitude of the scattering length and the occurrence of shape resonances in higher partial waves of the van der Waals system. We develop a mass-scaled model of the excited-state potential that represents the experimental data for different isotopes. The shape of the rotational photoassociation spectrum for various bosonic Yb isotopes can be qualitatively different.
We model the binding energies of rovibrational levels of the RbYb molecule using experimental data from two-color photoassociation spectroscopy in mixtures of ultracold
87Rb with various Yb isotopes. The model uses a theoretical potential based on state-of-the-art ab initio potentials, further improved by least-squares fitting to the experimental data. We have fixed the number of bound states supported by the potential curve, so that the model is mass scaled, that is, it accurately describes the bound-state energies for all measured isotopic combinations. Such a model enables an accurate prediction of the
s-wave scattering lengths of all isotopic combinations of the RbYb system. The reduced mass range is broad enough to cover the full scattering lengths range from $\ensuremath{-}\ensuremath{\infty}$ to $+\ensuremath{\infty}$. For example, the
87Rb
174Yb system is characterized by a large positive scattering length of
+880(120) a.u., while
87Rb
173Yb has $a=\ensuremath{-}626(88)$ a.u. On the other hand
87Rb
170Yb has a very small scattering length of $\ensuremath{-}11.5(2.5)$ a.u. confirmed by the pair's extremely low thermalization rate. For isotopic combinations including
85Rb the variation of the interspecies scattering lengths is much smoother ranging from
+39.0(1.6) a.u. for
85Rb
176Yb to
+230(12) a.u. in the case of
85Rb
168Yb. Hyperfine corrections to these scattering lengths are also given. We further complement the fitted potential with interaction parameters calculated from alternative methods. The recommended value of the van der Waals coefficient is
C6=2837(13) a.u. agrees with but is more precise than the current state-of-the-art theoretical predictions [M. S. Safronova, S. G. Porsev, and C. W. Clark, Phys. Rev. Lett. 109, 230802 (2012)].
For elastic scattering of 133 Cs atoms by 85 Rb and 87 Rb atoms, interacting via the X 1 Σ + and a 3 Σ + molecular states of RbCs, calculations are presented of the scattering length and the effective range and also of two volume parameters, one for low energy p-wave scattering and one for the energy of an ensemble of fermions. The calculations are performed by various methods, with several representations of the interatomic potentials, including new ab initio potentials presented here. It is shown how the calculated data may be corrected to include the influence of the long range interactions, thus removing the need for numerical solutions of the radial Schrödinger equation at very large interatomic separations. The sensitivity of the results to the choice of potentials, to the van der Waals dispersion coefficient C 6 and to the reduced mass of the colliding atoms is explored, and is found to be great.
The modified static exchange model (MSEM) recently introduced by Ray [1] to study two-atomic collision processes at low and cold-energies, is used for detailed analysis of the long-range effects due to induced dipole-dipole van der Waals interaction between Ps and H atoms. The MSEM includes the non-adiabatic short-range effect due to electron-exchange and the long-range effect due to induced dynamic dipole polarisabilities of the atoms. The effective interatomic potential is highly sensitive to the minimum distance between the atoms ( ). The s-, p- and d- wave elastic phase shifts, corresponding partial cross sections, the scattering length and effective ranges are calculated and studied with the variation of the chosen least interatomic distance between them. It is found that the scattering length is highly sensitive to the effective interatomic potential that depends on the least interatomic distance. In addition the studies are made in search of Feshbach resonances. The observed interesting feature with the variation of in the triplet channel invites more accurate investigations if new physics.
We report close-coupling (CC) quantum dynamics calculations for collisional excitation/de-excitation of the lowest four rotational levels of OD − and of OH − interacting with Rb atoms in a cold ion trap. The calculations are carried out over a range of energies capable of yielding the corresponding rates for state-changing events over a rather broad interval of temperatures which cover those reached in earlier cold trap experiments. They involved sympathetic cooling of the molecular anion through a cloud of laser-cooled Rb atoms, an experiment which is currently being run again through a Heidelberg–Innsbruck collaboration. The significance of isotopic effects is analysed by comparing both systems and the range of temperatures examined in the calculations is extended up to 400 K, starting from a few mK. Both cross sections and rates are found to be markedly larger than in the case of OD − /OH − interacting the He atoms under the same conditions, and the isotopic effects are also seen to be rather significant at the energies examined in the present study. Such findings are discussed in the light of the observed trap losses of molecular anions.