Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1801.07978 · Physical Review A

Atom-molecule collisions, spin relaxation, and sympathetic cooling in an ultracold spin-polarized Rb(S2)−SrF(Σ+2) mixture

Masato Morita, Maciej B. Kosicki, Piotr Szymon Żuchowski, Timur V. Tscherbul

Published Oct 9, 2018• 34 citations
arXivHTMLPDF

Abstract

We explore the suitability of ultracold collisions between spin-polarized $\mathrm{SrF}(^{2}\mathrm{\ensuremath{\Sigma}}^{+})$ molecules and $\mathrm{Rb}(^{2}S)$ atoms as elementary steps for the sympathetic cooling of $\mathrm{SrF}(^{2}\mathrm{\ensuremath{\Sigma}}^{+})$ molecules in a magnetic trap. To this end, we carry out quantum-mechanical scattering calculations on ultracold Rb + SrF collisions in a magnetic field based on an accurate potential-energy surface for the triplet electronic state of Rb-SrF developed ab initio using a spin-restricted coupled cluster method with single, double, and noniterative triple excitations [RCCSD(T)]. The Rb-SrF interaction has a global minimum with a well depth of 3444 ${\mathrm{cm}}^{\ensuremath{-}1}$ in a bent geometry and a shallow local minimum in the linear geometry. Despite such a strong and anisotropic interaction, we find that converged close-coupling scattering calculations on Rb + SrF collisions in a magnetic field are still possible using rotational basis sets including up to 125 closed rotational channels in the total angular momentum representation. Our calculations show that electronic spin relaxation in fully spin-polarized Rb-SrF collisions occurs much more slowly than elastic scattering over a wide range of magnetic fields (1--1000 G) and collision energies (${10}^{\ensuremath{-}5}--{10}^{\ensuremath{-}3}$ K), suggesting good prospects of sympathetic cooling into the microkelvin regime of laser-cooled $\mathrm{SrF}(^{2}\mathrm{\ensuremath{\Sigma}}^{+})$ molecules with spin-polarized $\mathrm{Rb}(^{2}S)$ atoms in a magnetic trap. We show that incoming $p$-wave scattering plays a significant role in ultracold collisions due to the large reduced mass of the Rb-SrF collision pair. The calculated magnetic-field dependence of the inelastic cross sections at $1.4\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}$ displays a rich resonance structure including a low-field $p$-wave resonance, which suggests that external magnetic fields can be used to enhance the efficiency of sympathetic cooling in heavy atom-molecule mixtures.

DOI
10.1103/physreva.98.042702

Related papers

Cold collisions of heavy Σ2 molecules with alkali-metal atoms in a magnetic field: Ab initio analysis and prospects for sympathetic cooling of SrOH(Σ+2) by Li(S2)

Masato Morita, Jacek A. Kłos, Alexei A. Buchachenko +1 more

We use accurate ab initio and quantum scattering calculations to explore the prospects for sympathetic cooling of the heavy molecular radical $\mathrm{SrOH}{(}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+})$ by ultracold Li atoms in a magnetic trap. Our ab initio calculations show that the chemical reaction between spin-polarized Li and SrOH, which occurs on the triplet Li-SrOH potential energy surface (PES), is strongly endothermic and hence energetically forbidden at ultralow temperatures. The chemical reaction $\mathrm{Li}(^{2}S)+\mathrm{SrOH}{(}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+})\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}\mathrm{Sr}(^{1}S)+\mathrm{LiOH}{(}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+})$ occurs barrierlessly on the singlet PES and is exothermic by 2505 ${\mathrm{cm}}^{\ensuremath{-}1}$. A two-dimensional PES for the triplet electronic state of Li-SrOH is calculated ab initio using the partially spin-restricted coupled cluster method with single, double, and perturbative triple excitations and a large correlation-consistent basis set. The highly anisotropic PES has a deep global minimum in the skewed Li-HOSr geometry with ${D}_{e}=4932\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and saddle points in collinear configurations. Our quantum scattering calculations predict low spin-relaxation rates in fully spin-polarized Li + SrOH collisions with the ratios of elastic to inelastic collision rates well in excess of 100 over a wide range of magnetic fields (1--1000 G) and collision energies (${10}^{\ensuremath{-}5}$ to 0.1 K), suggesting favorable prospects for sympathetic cooling of SrOH molecules with spin-polarized Li atoms in a magnetic trap. We find that spin relaxation in Li + SrOH collisions occurs via a direct mechanism mediated by the magnetic dipole-dipole interaction between the electron spins of Li and SrOH, and that the indirect (spin-rotation) mechanism is strongly suppressed. The upper limit to the Li + SrOH reaction rate coefficient calculated for the singlet PES using adiabatic capture theory is found to decrease from $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{3}$/s to a limiting value of $3.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{3}$/s with decreasing temperature from 0.1 K to 1 $\ensuremath{\mu}\mathrm{K}$.

arXiv:1702.05856•Physical Review A•Jun 26, 2017•22 citations

Ultracold spin-polarized mixtures of 2Σ molecules with S -state atoms: Collisional stability and implications for sympathetic cooling

Timur V. Tscherbul, Jacek A. Kłos, Alexei A. Buchachenko

The prospects of sympathetic cooling of polar molecules with magnetically cotrapped alkali-metal atoms are generally considered poor due to strongly anisotropic atom-molecule interactions leading to large spin relaxation rates. Using rigorous quantum scattering calculations based on ab initio interaction potentials, we show that inelastic spin relaxation in low-temperature collisions of CaH(${}^{2}\ensuremath{\Sigma}$) molecules with Li and Mg atoms occurs at a slow rate despite the strongly anisotropic interactions. This unexpected result, which we rationalize using multichannel quantum-defect theory, opens up the possibility of sympathetic cooling of polar ${}^{2}\ensuremath{\Sigma}$ molecules with alkali-metal atoms in a magnetic trap and with alkaline-earth-metal atoms in an optical dipole trap.

arXiv:1106.1492•Physical Review A•Oct 28, 2011•49 citations

Low-energy collisions of NH3 and ND3 with ultracold Rb atoms

Piotr Szymon Żuchowski, Jeremy M. Hutson

We carry out quantum inelastic scattering calculations of collisions of Rb atoms with inverting ${\text{NH}}_{3}$ and ${\text{ND}}_{3}$ molecules in the energy range between 0 and $100\text{ }{\text{cm}}^{\ensuremath{-}1}$, which are important for experiments using velocity-controlled molecular beams to probe scattering resonances. We focus on molecules initially in the upper level of the ammonia inversion doublet for $j=1$, $k=1$, which is low-field seeking and can be controlled in a Stark decelerator. We calculate the integral elastic and state-to-state inelastic cross sections in the coupled-states approximation. We demonstrate the presence of both shape and Feshbach resonances in the elastic and inelastic cross sections at low collision energies and discuss their origin in terms of the bound states of the Rb-${\text{ND}}_{3}$ complex. We also consider elastic and inelastic cross sections in the ultracold regime, using close-coupling calculations, in order to assess the viability of sympathetic cooling of ${\text{ND}}_{3}$ by Rb. The inelastic cross section for relaxation to the lower level of the inversion doublet is smaller than expected for such a strongly coupled system but is still likely to be too large to allow sympathetic cooling for ${\text{ND}}_{3}$ in low-field-seeking states. However, there is a good prospect that sympathetic cooling will be possible for molecules in high-field-seeking states even when the collision partner is a magnetically trapped atom in a low-field-seeking state.

arXiv:0902.4548•Physical Review A•Jun 11, 2009•57 citations

Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + ${\rm CH}_2(\tilde{X})$ CH 2(X) collisions

Timur V. Tscherbul, Timur A. Grinev, Hua‐Gen Yu +4 more

We develop a rigorous quantum mechanical theory for collisions of polyatomic molecular radicals with S-state atoms in the presence of an external magnetic field. The theory is based on a fully uncoupled space-fixed basis set representation of the multichannel scattering wave function. Explicit expressions are presented for the matrix elements of the scattering Hamiltonian for spin-1/2 and spin-1 polyatomic molecular radicals interacting with structureless targets. The theory is applied to calculate the cross sections and thermal rate constants for spin relaxation in low-temperature collisions of the prototypical organic molecule methylene [CH(2)(X(3)B(1))] with He atoms. To this end, two accurate three-dimensional potential energy surfaces (PESs) of the He-CH(2)(X(3)B(1)) complex are developed using the state-of-the-art coupled-cluster method including single and double excitations along with a perturbative correction for triple excitations and large basis sets. Both PESs exhibit shallow minima and are weakly anisotropic. Our calculations show that spin relaxation in collisions of CH(2), CHD, and CD(2) molecules with He atoms occurs at a much slower rate than elastic scattering over a large range of temperatures (1 μK-1 K) and magnetic fields (0.01-1 T), suggesting excellent prospects for cryogenic helium buffer-gas cooling of ground-state ortho-CH(2)(X(3)B(1)) molecules in a magnetic trap. Furthermore, we find that ortho-CH(2) undergoes collision-induced spin relaxation much more slowly than para-CH(2), which indicates that magnetic trapping can be used to separate nuclear spin isomers of open-shell polyatomic molecules.

arXiv:1209.3071•The Journal of Chemical Physics•Sep 10, 2012•10 citations

Sympathetic cooling of the Ba + ion by collisions with ultracold Rb atoms: Theoretical prospects

Michał Krych, Wojciech Skomorowski, Filip Pawłowski +2 more

State-of-the-art ab initio techniques have been applied to compute the potential energy curves of the (BaRb)${}^{+}$ molecular ion in the Born-Oppenheimer approximation for the singlet and triplet states dissociating into the ground-state ${}^{1}$$S$ Rb${}^{+}$ ion and the Ba atom in the ground ${}^{1}$$S$ state or the lowest singlet or triplet $d$ excited states, and for the singlet and triplet states dissociating into the ground-state ${}^{2}$$S$ Rb atom and the ground-state ${}^{2}$$S$ Ba${}^{+}$ ion. The ground-state potential energy was obtained with the coupled-cluster method restricted to single, double, and nonperturbative triple excitations. The first triplet states in the $\ensuremath{\Sigma}$, $\ensuremath{\Pi}$, and $\ensuremath{\Delta}$ symmetries were computed with the restricted open-shell coupled-cluster method restricted to single, double, and nonperturbative triple excitations. All other excited-state potential energy curves were computed using the equation of motion approach within the coupled-cluster singles, doubles, and linear triples framework. The long-range coefficients describing the electrostatic, induction, and dispersion interactions at large interatomic distances are also reported. The electric transition dipole moments governing the $x$ ${}^{1}\ensuremath{\Sigma}\ensuremath{\rightarrow}{}^{1}\ensuremath{\Sigma},{}^{1}\ensuremath{\Pi}$ transitions have been obtained as the first residue of the polarization propagator computed with the linear response coupled-cluster method restricted to single and double excitations. Nonadiabatic radial and angular coupling matrix elements as well as the spin-orbit coupling matrix elements have been evaluated using the multireference configuration-interaction method restricted to single and double excitations with a large active space. With these couplings, the spin-orbit-coupled (relativistic) potential energy curves for the 0${}^{+}$ and 1 states relevant for the running experiments have been obtained. Finally, relativistic transition moments and nonadiabatic coupling matrix elements were obtained from the nonrelativistic results and spin-orbit eigenvectors. The electronic structure input has been employed in the single-channel scattering calculations of the collisional cross sections between the Ba${}^{+}$ ion and Rb atom. Both nonrelativistic and relativistic potentials were used in these calculations. Our results show that the inelastic cross section corresponding to the charge transfer from the Rb atom to the Ba${}^{+}$ ion is much smaller than the elastic one over a wide range of energies up to 1 mK. This suggests that sympathetic cooling of the Ba${}^{+}$ ion by collisions with ultracold Rb atoms should be possible.

arXiv:1008.0840•Physical Review A•Mar 31, 2011•60 citations

Sympathetic cooling of fluorine atoms with ultracold atomic hydrogen

Maykel Leonardo González-Martínez, Jeremy M. Hutson

We consider the prospect of using ultracold hydrogen atoms for sympathetic cooling of fluorine atoms to microkelvin temperatures. We carry out quantum-mechanical calculations on collisions between cold F and H atoms in magnetically trappable states and show that the ratio of elastic to inelastic cross sections remains high across a wide range of temperatures and magnetic fields. For F atoms initially in the spin-stretched state (${}^{2}{P}_{3/2}$, $f={m}_{f}=+2$), sympathetic cooling appears likely to succeed from starting temperatures around 1 K or even higher. This occurs because inelastic collisions are suppressed by $p$-wave and $d$-wave barriers that are 600 mK and 3.2 K high, respectively. In combination with recent results on $\mathrm{H}+\mathrm{NH}$ and $\mathrm{H}+\mathrm{OH}$ collisions [M. L. Gonz\'alez-Mart\'{\i}nez and J. M. Hutson, Phys. Rev. Lett. 111, 203004 (2013)], this establishes ultracold H atoms as a very promising and versatile coolant for atoms and molecules that cannot be laser-cooled.

arXiv:1310.4357•Physical Review A•Nov 20, 2013•8 citations
We explore the suitability of ultracold collisions between spin-polarized SrF(2\ensuremathΣ+)\mathrm{SrF}(^{2}\mathrm{\ensuremath{\Sigma}}^{+})SrF(2\ensuremathΣ+) molecules and Rb(2S)\mathrm{Rb}(^{2}S)Rb(2S) atoms as elementary steps for the sympathetic cooling of SrF(2\ensuremathΣ+)\mathrm{SrF}(^{2}\mathrm{\ensuremath{\Sigma}}^{+})SrF(2\ensuremathΣ+) molecules in a magnetic trap. To this end, we carry out quantum-mechanical scattering calculations on ultracold Rb + SrF collisions in a magnetic field based on an accurate potential-energy surface for the triplet electronic state of Rb-SrF developed ab initio using a spin-restricted coupled cluster method with single, double, and noniterative triple excitations [RCCSD(T)]. The Rb-SrF interaction has a global minimum with a well depth of 3444 cm\ensuremath−1{\mathrm{cm}}^{\ensuremath{-}1}cm\ensuremath−1 in a bent geometry and a shallow local minimum in the linear geometry. Despite such a strong and anisotropic interaction, we find that converged close-coupling scattering calculations on Rb + SrF collisions in a magnetic field are still possible using rotational basis sets including up to 125 closed rotational channels in the total angular momentum representation. Our calculations show that electronic spin relaxation in fully spin-polarized Rb-SrF collisions occurs much more slowly than elastic scattering over a wide range of magnetic fields (1--1000 G) and collision energies (10\ensuremath−5−−10\ensuremath−3{10}^{\ensuremath{-}5}--{10}^{\ensuremath{-}3}10\ensuremath−5−−10\ensuremath−3 K), suggesting good prospects of sympathetic cooling into the microkelvin regime of laser-cooled SrF(2\ensuremathΣ+)\mathrm{SrF}(^{2}\mathrm{\ensuremath{\Sigma}}^{+})SrF(2\ensuremathΣ+) molecules with spin-polarized Rb(2S)\mathrm{Rb}(^{2}S)Rb(2S) atoms in a magnetic trap. We show that incoming ppp-wave scattering plays a significant role in ultracold collisions due to the large reduced mass of the Rb-SrF collision pair. The calculated magnetic-field dependence of the inelastic cross sections at 1.4\ensuremathμK1.4\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{K}1.4\ensuremathμK displays a rich resonance structure including a low-field ppp-wave resonance, which suggests that external magnetic fields can be used to enhance the efficiency of sympathetic cooling in heavy atom-molecule mixtures.
We use accurate ab initio and quantum scattering calculations to explore the prospects for sympathetic cooling of the heavy molecular radical $\mathrm{SrOH}{(}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+})$ by ultracold Li atoms in a magnetic trap. Our ab initio calculations show that the chemical reaction between spin-polarized Li and SrOH, which occurs on the triplet Li-SrOH potential energy surface (PES), is strongly endothermic and hence energetically forbidden at ultralow temperatures. The chemical reaction $\mathrm{Li}(^{2}S)+\mathrm{SrOH}{(}^{2}{\mathrm{\ensuremath{\Sigma}}}^{+})\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}\mathrm{Sr}(^{1}S)+\mathrm{LiOH}{(}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+})$ occurs barrierlessly on the singlet PES and is exothermic by 2505 ${\mathrm{cm}}^{\ensuremath{-}1}$. A two-dimensional PES for the triplet electronic state of Li-SrOH is calculated ab initio using the partially spin-restricted coupled cluster method with single, double, and perturbative triple excitations and a large correlation-consistent basis set. The highly anisotropic PES has a deep global minimum in the skewed Li-HOSr geometry with ${D}_{e}=4932\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and saddle points in collinear configurations. Our quantum scattering calculations predict low spin-relaxation rates in fully spin-polarized Li + SrOH collisions with the ratios of elastic to inelastic collision rates well in excess of 100 over a wide range of magnetic fields (1--1000 G) and collision energies (${10}^{\ensuremath{-}5}$ to 0.1 K), suggesting favorable prospects for sympathetic cooling of SrOH molecules with spin-polarized Li atoms in a magnetic trap. We find that spin relaxation in Li + SrOH collisions occurs via a direct mechanism mediated by the magnetic dipole-dipole interaction between the electron spins of Li and SrOH, and that the indirect (spin-rotation) mechanism is strongly suppressed. The upper limit to the Li + SrOH reaction rate coefficient calculated for the singlet PES using adiabatic capture theory is found to decrease from $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{3}$/s to a limiting value of $3.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{3}$/s with decreasing temperature from 0.1 K to 1 $\ensuremath{\mu}\mathrm{K}$.
The prospects of sympathetic cooling of polar molecules with magnetically cotrapped alkali-metal atoms are generally considered poor due to strongly anisotropic atom-molecule interactions leading to large spin relaxation rates. Using rigorous quantum scattering calculations based on ab initio interaction potentials, we show that inelastic spin relaxation in low-temperature collisions of CaH(${}^{2}\ensuremath{\Sigma}$) molecules with Li and Mg atoms occurs at a slow rate despite the strongly anisotropic interactions. This unexpected result, which we rationalize using multichannel quantum-defect theory, opens up the possibility of sympathetic cooling of polar ${}^{2}\ensuremath{\Sigma}$ molecules with alkali-metal atoms in a magnetic trap and with alkaline-earth-metal atoms in an optical dipole trap.
We carry out quantum inelastic scattering calculations of collisions of Rb atoms with inverting NH3{\text{NH}}_{3}NH3​ and ND3{\text{ND}}_{3}ND3​ molecules in the energy range between 0 and $100\text{ }{\text{cm}}^{\ensuremath{-}1}$, which are important for experiments using velocity-controlled molecular beams to probe scattering resonances. We focus on molecules initially in the upper level of the ammonia inversion doublet for j=1j=1j=1, k=1k=1k=1, which is low-field seeking and can be controlled in a Stark decelerator. We calculate the integral elastic and state-to-state inelastic cross sections in the coupled-states approximation. We demonstrate the presence of both shape and Feshbach resonances in the elastic and inelastic cross sections at low collision energies and discuss their origin in terms of the bound states of the Rb-ND3{\text{ND}}_{3}ND3​ complex. We also consider elastic and inelastic cross sections in the ultracold regime, using close-coupling calculations, in order to assess the viability of sympathetic cooling of ND3{\text{ND}}_{3}ND3​ by Rb. The inelastic cross section for relaxation to the lower level of the inversion doublet is smaller than expected for such a strongly coupled system but is still likely to be too large to allow sympathetic cooling for ND3{\text{ND}}_{3}ND3​ in low-field-seeking states. However, there is a good prospect that sympathetic cooling will be possible for molecules in high-field-seeking states even when the collision partner is a magnetically trapped atom in a low-field-seeking state.
Cold collisions of polyatomic molecular radicals with S-state atoms in a magnetic field: An ab initio study of He + CH2(X~){\rm CH}_2(\tilde{X})CH2​(X~) CH 2(X) collisions
We develop a rigorous quantum mechanical theory for collisions of polyatomic molecular radicals with S-state atoms in the presence of an external magnetic field. The theory is based on a fully uncoupled space-fixed basis set representation of the multichannel scattering wave function. Explicit expressions are presented for the matrix elements of the scattering Hamiltonian for spin-1/2 and spin-1 polyatomic molecular radicals interacting with structureless targets. The theory is applied to calculate the cross sections and thermal rate constants for spin relaxation in low-temperature collisions of the prototypical organic molecule methylene [CH(2)(X(3)B(1))] with He atoms. To this end, two accurate three-dimensional potential energy surfaces (PESs) of the He-CH(2)(X(3)B(1)) complex are developed using the state-of-the-art coupled-cluster method including single and double excitations along with a perturbative correction for triple excitations and large basis sets. Both PESs exhibit shallow minima and are weakly anisotropic. Our calculations show that spin relaxation in collisions of CH(2), CHD, and CD(2) molecules with He atoms occurs at a much slower rate than elastic scattering over a large range of temperatures (1 μK-1 K) and magnetic fields (0.01-1 T), suggesting excellent prospects for cryogenic helium buffer-gas cooling of ground-state ortho-CH(2)(X(3)B(1)) molecules in a magnetic trap. Furthermore, we find that ortho-CH(2) undergoes collision-induced spin relaxation much more slowly than para-CH(2), which indicates that magnetic trapping can be used to separate nuclear spin isomers of open-shell polyatomic molecules.
State-of-the-art ab initio techniques have been applied to compute the potential energy curves of the (BaRb)+{}^{+}+ molecular ion in the Born-Oppenheimer approximation for the singlet and triplet states dissociating into the ground-state 1{}^{1}1SSS Rb+{}^{+}+ ion and the Ba atom in the ground 1{}^{1}1SSS state or the lowest singlet or triplet ddd excited states, and for the singlet and triplet states dissociating into the ground-state 2{}^{2}2SSS Rb atom and the ground-state 2{}^{2}2SSS Ba+{}^{+}+ ion. The ground-state potential energy was obtained with the coupled-cluster method restricted to single, double, and nonperturbative triple excitations. The first triplet states in the $\ensuremath{\Sigma}$, $\ensuremath{\Pi}$, and $\ensuremath{\Delta}$ symmetries were computed with the restricted open-shell coupled-cluster method restricted to single, double, and nonperturbative triple excitations. All other excited-state potential energy curves were computed using the equation of motion approach within the coupled-cluster singles, doubles, and linear triples framework. The long-range coefficients describing the electrostatic, induction, and dispersion interactions at large interatomic distances are also reported. The electric transition dipole moments governing the xxx ${}^{1}\ensuremath{\Sigma}\ensuremath{\rightarrow}{}^{1}\ensuremath{\Sigma},{}^{1}\ensuremath{\Pi}$ transitions have been obtained as the first residue of the polarization propagator computed with the linear response coupled-cluster method restricted to single and double excitations. Nonadiabatic radial and angular coupling matrix elements as well as the spin-orbit coupling matrix elements have been evaluated using the multireference configuration-interaction method restricted to single and double excitations with a large active space. With these couplings, the spin-orbit-coupled (relativistic) potential energy curves for the 0+{}^{+}+ and 1 states relevant for the running experiments have been obtained. Finally, relativistic transition moments and nonadiabatic coupling matrix elements were obtained from the nonrelativistic results and spin-orbit eigenvectors. The electronic structure input has been employed in the single-channel scattering calculations of the collisional cross sections between the Ba+{}^{+}+ ion and Rb atom. Both nonrelativistic and relativistic potentials were used in these calculations. Our results show that the inelastic cross section corresponding to the charge transfer from the Rb atom to the Ba+{}^{+}+ ion is much smaller than the elastic one over a wide range of energies up to 1 mK. This suggests that sympathetic cooling of the Ba+{}^{+}+ ion by collisions with ultracold Rb atoms should be possible.
We consider the prospect of using ultracold hydrogen atoms for sympathetic cooling of fluorine atoms to microkelvin temperatures. We carry out quantum-mechanical calculations on collisions between cold F and H atoms in magnetically trappable states and show that the ratio of elastic to inelastic cross sections remains high across a wide range of temperatures and magnetic fields. For F atoms initially in the spin-stretched state (2P3/2{}^{2}{P}_{3/2}2P3/2​, f=mf=+2f={m}_{f}=+2f=mf​=+2), sympathetic cooling appears likely to succeed from starting temperatures around 1 K or even higher. This occurs because inelastic collisions are suppressed by ppp-wave and ddd-wave barriers that are 600 mK and 3.2 K high, respectively. In combination with recent results on H+NH\mathrm{H}+\mathrm{NH}H+NH and H+OH\mathrm{H}+\mathrm{OH}H+OH collisions [M. L. Gonz\'alez-Mart\'{\i}nez and J. M. Hutson, Phys. Rev. Lett. 111, 203004 (2013)], this establishes ultracold H atoms as a very promising and versatile coolant for atoms and molecules that cannot be laser-cooled.