Physical Review A

Cold collisions between atoms and diatomic molecules

Marius Lysebo, Leif Veseth

Published Mar 24, 2008• 15 citations

Abstract

Collision cross sections are calculated for the three systems ${\text{O}}_{2}\text{-He}$, ${\text{Na}}_{2}\text{-Na}$ and ${\text{K}}_{2}\text{-K}$ at cold and ultracold temperatures. We discuss their relevance for cold molecule formation by buffer-gas cooling and by other cooling methods where collisions between molecules and atoms are important, e.g photoassociation. The molecule is treated as a rigid rotator in the electronic and vibrational ground state. We have calculated ab initio the potential energy surfaces for the three systems with special emphasis on the long range potential which is very important at low energies. With relevance to buffer gas cooling, we have also studied the thermalization process between ${\text{O}}_{2}$ molecules and He atoms as determined by the calculated cross sections.

DOI: 10.1103/physreva.77.032721

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Physical Review A

Cold collisions between atoms and diatomic molecules

Marius Lysebo, Leif Veseth

Published Mar 24, 2008• 15 citations

Publisher

Abstract

Collision cross sections are calculated for the three systems

{\text{O}}_{2}\text{-He}

{\text{Na}}_{2}\text{-Na}

and

{\text{K}}_{2}\text{-K}

at cold and ultracold temperatures. We discuss their relevance for cold molecule formation by buffer-gas cooling and by other cooling methods where collisions between molecules and atoms are important, e.g photoassociation. The molecule is treated as a rigid rotator in the electronic and vibrational ground state. We have calculated ab initio the potential energy surfaces for the three systems with special emphasis on the long range potential which is very important at low energies. With relevance to buffer gas cooling, we have also studied the thermalization process between

{\text{O}}_{2}

molecules and He atoms as determined by the calculated cross sections.

DOI: 10.1103/physreva.77.032721

Related papers

Collisional Cooling of Polar Diatomics in 3He and 4He Buffer Gas: A Quantum Calculation at Ultralow Energies

Enrico Bodo, Franco Antonio Gianturco

The anisotropic interactions of three polar molecules CO, HF, and LiH with He atoms (in their ground electronic states), obtained from accurate ab initio calculations that explicitly include their vibration-to-translation coupling terms are analyzed in detail, to compare their relative features. The quantum scattering calculations of their rotovibrational inelastic cross sections are conducted using a recently proposed multichannel treatment, the modified variable phase method, that has been implemented by the authors and applied here to ultralow collision energies. A comparison of the different relaxation efficiencies exhibited by the three title molecules in releasing their internal vibrational energy during ultracold collisions with 4 He and 3 He buffer gas is performed in detail and specific suggestions for experimental choices are extracted from these findings.The anisotropic interactions of three polar molecules CO, HF, and LiH with He atoms (in their ground electronic states), obtained from accurate ab initio calculations that explicitly include their vibration-to-translation coupling terms are analyzed in detail, to compare their relative features. The quantum scattering calculations of their rotovibrational inelastic cross sections are conducted using a recently proposed multichannel treatment, the modified variable phase method, that has been implemented by the authors and applied here to ultralow collision energies. A comparison of the different relaxation efficiencies exhibited by the three title molecules in releasing their internal vibrational energy during ultracold collisions with 4 He and 3 He buffer gas is performed in detail and specific suggestions for experimental choices are extracted from these findings.

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A close coupling quantum-mechanical calculation is performed for rotational energy transfer in a HD+HD collision at very low energy, down to the ultracold temperatures: $T\ensuremath{\sim}{10}^{\ensuremath{-}8}$ K. A global six-dimensional H ${}_{2}$ -H ${}_{2}$ potential-energy surface is adopted from a previous work [Boothroyd et al., J. Chem. Phys. 116, 666 (2002)]. State-resolved integral cross sections ${\ensuremath{\sigma}}_{ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}}({\ensuremath{\varepsilon}}_{\text{kin}})$ of different quantum-mechanical rotational transitions $ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}$ in the HD molecules and corresponding state-resolved thermal rate coefficients ${k}_{ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}}(T)$ have been computed. Additionally, for comparison, H ${}_{2}$ +H ${}_{2}$ calculations for a few selected rotational transitions have also been performed. The hydrogen and deuterated hydrogen molecules are treated as rigid rotors in this work. A pronounced isotope effect is identified in the cross sections of these collisions at low and ultracold temperatures.A close coupling quantum-mechanical calculation is performed for rotational energy transfer in a HD+HD collision at very low energy, down to the ultracold temperatures: $T\ensuremath{\sim}{10}^{\ensuremath{-}8}$ K. A global six-dimensional H${}_{2}$-H${}_{2}$ potential-energy surface is adopted from a previous work [Boothroyd et al., J. Chem. Phys. 116, 666 (2002)]. State-resolved integral cross sections ${\ensuremath{\sigma}}_{ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}}({\ensuremath{\varepsilon}}_{\text{kin}})$ of different quantum-mechanical rotational transitions $ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}$ in the HD molecules and corresponding state-resolved thermal rate coefficients ${k}_{ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}}(T)$ have been computed. Additionally, for comparison, H${}_{2}$+H${}_{2}$ calculations for a few selected rotational transitions have also been performed. The hydrogen and deuterated hydrogen molecules are treated as rigid rotors in this work. A pronounced isotope effect is identified in the cross sections of these collisions at low and ultracold temperatures.

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Creating ultracold molecules by collisions with ultracold rare-gas atoms in an optical trap

Paolo Barletta, Jonathan Tennyson, P. F. Barker

We study collisions of para- ${\mathrm{H}}_{2}$ with five rare-gas atomic species (He, Ne, Ar, Kr, and Xe) over the range from $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and evaluate the feasibility of sympathetic cooling ${\mathrm{H}}_{2}$ with ultracold ground state rare-gas atoms co-trapped within a deep optical trap. Collision cross sections over this large temperature range show that all of these species could be used to cool ${\mathrm{H}}_{2}$ to ultracold temperatures and that argon and helium are the most promising species for future experiments. A simple yet accurate method for calculating the microscopic observables needed in the present analysis is also described, as well as the sensitivity of the calculated cross sections to the potential energy surface used.We study collisions of para-${\mathrm{H}}_{2}$ with five rare-gas atomic species (He, Ne, Ar, Kr, and Xe) over the range from $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and evaluate the feasibility of sympathetic cooling ${\mathrm{H}}_{2}$ with ultracold ground state rare-gas atoms co-trapped within a deep optical trap. Collision cross sections over this large temperature range show that all of these species could be used to cool ${\mathrm{H}}_{2}$ to ultracold temperatures and that argon and helium are the most promising species for future experiments. A simple yet accurate method for calculating the microscopic observables needed in the present analysis is also described, as well as the sensitivity of the calculated cross sections to the potential energy surface used.

arXiv:0806.1196Physical Review ANov 13, 200826 citations

Collision cross sections are calculated for the three systems

{\text{O}}_{2}\text{-He}

{\text{Na}}_{2}\text{-Na}

and

{\text{K}}_{2}\text{-K}

{\text{O}}_{2}

molecules and He atoms as determined by the calculated cross sections.

{}_{2}

-H

{}_{2}

potential-energy surface is adopted from a previous work [Boothroyd et al., J. Chem. Phys. 116, 666 (2002)]. State-resolved integral cross sections ${\ensuremath{\sigma}}_{ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}}({\ensuremath{\varepsilon}}_{\text{kin}})$ of different quantum-mechanical rotational transitions $ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}$ in the HD molecules and corresponding state-resolved thermal rate coefficients ${k}_{ij\ensuremath{\rightarrow}{i}^{\ensuremath{'}}{j}^{\ensuremath{'}}}(T)$ have been computed. Additionally, for comparison, H

{}_{2}

{}_{2}

calculations for a few selected rotational transitions have also been performed. The hydrogen and deuterated hydrogen molecules are treated as rigid rotors in this work. A pronounced isotope effect is identified in the cross sections of these collisions at low and ultracold temperatures.

We study collisions of para-

{\mathrm{H}}_{2}

with five rare-gas atomic species (He, Ne, Ar, Kr, and Xe) over the range from $1\phantom{\rule{0.3em}{0ex}}\mathrm{K}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and evaluate the feasibility of sympathetic cooling

{\mathrm{H}}_{2}

with ultracold ground state rare-gas atoms co-trapped within a deep optical trap. Collision cross sections over this large temperature range show that all of these species could be used to cool

{\mathrm{H}}_{2}

to ultracold temperatures and that argon and helium are the most promising species for future experiments. A simple yet accurate method for calculating the microscopic observables needed in the present analysis is also described, as well as the sensitivity of the calculated cross sections to the potential energy surface used.