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

Physical Review A

Low-temperature collisions of NH(X3Σ−) molecules with He atoms in a magnetic field: Anab initiostudy

Roman V. Krems, H. R. Sadeghpour, A. Dalgarno, Dominika Zgid, Jacek A. Kłos, Grzegorz Chałasiński

Published Nov 12, 2003• 72 citations
Publisher

Abstract

Ab initio calculations of cross sections and rate constants for elastic scattering and Zeeman relaxation in collisions of $\mathrm{NH}(X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}})$ molecules with ${}^{3}\mathrm{He}$ atoms in a magnetic field are presented and the mechanism for Zeeman transitions in ground-state ${}^{3}\ensuremath{\Sigma}$ molecules is established. The potential surface for He-NH interaction is obtained using all-electron coupled-cluster calculations with single, double, and noniterative triple excitations in a basis set augmented by bond functions. The ratio of the rates for elastic energy transfer and Zeeman relaxation in NH-${}^{3}\mathrm{He}$ collisions exceeds ${10}^{5}$ at temperatures between $0.5$ and 1 K.

DOI
10.1103/physreva.68.051401

Related papers

Interaction of NH(XΣ−3) with He: Potential energy surface, bound states, and collisional Zeeman relaxation

Hubert Cybulski, Roman V. Krems, H. R. Sadeghpour +6 more

A detailed analysis of the He-NH((3)Sigma(-)) van der Waals complex is presented. We discuss ab initio calculations of the potential energy surface and fitting procedures with relevance to cold collisions, and we present accurate calculations of bound energy levels of the triatomic complex as well as collisional properties of NH molecules in a buffer gas of (3)He. The influence of the external magnetic field used to trap the NH molecules and the effect of the atom-molecule interaction potential on the collisionally induced Zeeman relaxation are explored. It is shown that minute variations of the interaction potential due to different fitting procedures may alter the Zeeman relaxation rate at ultralow temperatures by as much as 50%.

The Journal of Chemical Physics•Feb 26, 2005•83 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

Elastic and inelastic collisions of 2Σ molecules in a magnetic field

Jie Cui, Roman V. Krems

We calculate the cross sections for elastic scattering and Zeeman relaxation in binary collisions of molecules in the rovibrational ground state of a ${}^{2}\ensuremath{\Sigma}$ electronic state and the Zeeman state with the electron spin projection ${M}_{S}=\frac{1}{2}$ on the magnetic field axis. This is the lowest-energy state of ${}^{2}\ensuremath{\Sigma}$ molecules confined in a magnetic trap. The results are averaged over calculations with multiple molecule-molecule interaction potentials, which yield the expectation intervals for the cross sections and the elastic-to-inelastic cross-section ratios. We find that the elastic-to-inelastic cross-section ratios under conditions corresponding to trapped molecular ensembles at $T\ensuremath{\sim}{10}^{\ensuremath{-}3}$ K exceed 100 for the majority of ${}^{2}\ensuremath{\Sigma}$ molecules. The range of ${}^{2}\ensuremath{\Sigma}$ molecules expected to be collisionally unstable in magnetic traps at $T<{10}^{\ensuremath{-}3}$ K is limited to molecules with the spin-rotation interaction constant ${\ensuremath{\gamma}}_{\mathrm{SR}}>0.5$ cm${}^{\ensuremath{-}1}$ and the rotational constant ${B}_{e}<4$ cm${}^{\ensuremath{-}1}$.

arXiv:1308.0771•Physical Review A•Oct 11, 2013•6 citations

Cold and ultracold NH–NH collisions: The field-free case

Liesbeth M. C. Janssen, Piotr Szymon Żuchowski, Ad van der Avoird +2 more

We present elastic and inelastic spin-changing cross sections for cold and ultracold NH(X (3)Σ(-)) + NH(X (3)Σ(-)) collisions, obtained from full quantum scattering calculations on an accurate ab initio quintet potential-energy surface. Although we consider only collisions in zero field, we focus on the cross sections relevant for magnetic trapping experiments. It is shown that evaporative cooling of both fermionic (14)NH and bosonic (15)NH is likely to be successful for hyperfine states that allow s-wave collisions. The calculated cross sections are very sensitive to the details of the interaction potential, due to the presence of (quasi)bound state resonances. The remaining inaccuracy of the ab initio potential-energy surface therefore gives rise to an uncertainty in the numerical cross-section values. However, based on a sampling of the uncertainty range of the ab initio calculations, we conclude that the exact potential is likely to be such that the elastic-to-inelastic cross-section ratio is sufficiently large to achieve efficient evaporative cooling. This likelihood is only weakly dependent on the size of the channel basis set used in the scattering calculations.

arXiv:1012.0804•The Journal of Chemical Physics•Mar 28, 2011•25 citations

Ab initiostudy of Tm-He interactions and dynamics in a magnetic trap

Alexei A. Buchachenko, Grzegorz Chałasiński, Małgorzata M. Szczęśniak +1 more

The dynamics of magnetic relaxation of Tm atoms in cold helium gas is investigated using ab initio interaction potentials between $\mathrm{Tm}(^{2}F)$ and He atoms. The interaction of $\mathrm{Tm}(^{2}F)$ with He gives rise to four adiabatic potentials of ${\ensuremath{\Sigma}}^{+}$, $\ensuremath{\Pi}$, $\ensuremath{\Delta}$, and $\ensuremath{\Phi}$ symmetries, which are found to be degenerate to within $0.1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ at all interatomic distances larger than $R=5.4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. The small splitting between the interaction potentials leads to suppression of Zeeman transitions in Tm-He collisions. Our quantum scattering calculations yield a small rate constant of $1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ for Zeeman relaxation of the $\mathrm{Tm}(^{2}F_{7∕2})$ atoms in the maximally stretched $M=7∕2$ sublevel at the temperature $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, in reasonable agreement with the measured value $(5.0\ifmmode\pm\else\textpm\fi{}2.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. The sensitivity of Zeeman-relaxation cross sections to details of the interaction potentials is examined. To our knowledge, this is one of only two comparisons of ab initio quantum scattering calculations with experimental measurements of inelastic collisions at subkelvin temperatures near one Kelvin. Our work thus demonstrates the feasibility of describing cold collisions from first principles.

Physical Review A•Aug 2, 2006•15 citations

Magnetic Trapping and Zeeman Relaxation of NH ( X Σ−3 )

Wesley C. Campbell, Edem Tsikata, Hsin-I Lu +2 more

NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with $^{3}\mathrm{He}$ is measured to be $3.8\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }{\mathrm{cm}}^{2}$ at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of $\ensuremath{\gamma}=7\ifmmode\times\else\texttimes\fi{}{10}^{4}$, in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K\l{}os, and G. Cha\l{}asi\ifmmode \acute{n}\else \'{n}\fi{}ski, Phys. Rev. A 68, 051401 (2003)].

arXiv:physics/0702071•Physical Review Letters•May 25, 2007•131 citations
Ab initio calculations of cross sections and rate constants for elastic scattering and Zeeman relaxation in collisions of NH(X3\ensuremathΣ\ensuremath−)\mathrm{NH}(X{}^{3}{\ensuremath{\Sigma}}^{\ensuremath{-}})NH(X3\ensuremathΣ\ensuremath−) molecules with 3He{}^{3}\mathrm{He}3He atoms in a magnetic field are presented and the mechanism for Zeeman transitions in ground-state 3\ensuremathΣ{}^{3}\ensuremath{\Sigma}3\ensuremathΣ molecules is established. The potential surface for He-NH interaction is obtained using all-electron coupled-cluster calculations with single, double, and noniterative triple excitations in a basis set augmented by bond functions. The ratio of the rates for elastic energy transfer and Zeeman relaxation in NH-3He{}^{3}\mathrm{He}3He collisions exceeds 105{10}^{5}105 at temperatures between 0.50.50.5 and 1 K.
A detailed analysis of the He-NH((3)Sigma(-)) van der Waals complex is presented. We discuss ab initio calculations of the potential energy surface and fitting procedures with relevance to cold collisions, and we present accurate calculations of bound energy levels of the triatomic complex as well as collisional properties of NH molecules in a buffer gas of (3)He. The influence of the external magnetic field used to trap the NH molecules and the effect of the atom-molecule interaction potential on the collisionally induced Zeeman relaxation are explored. It is shown that minute variations of the interaction potential due to different fitting procedures may alter the Zeeman relaxation rate at ultralow temperatures by as much as 50%.
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.
We calculate the cross sections for elastic scattering and Zeeman relaxation in binary collisions of molecules in the rovibrational ground state of a ${}^{2}\ensuremath{\Sigma}$ electronic state and the Zeeman state with the electron spin projection MS=12{M}_{S}=\frac{1}{2}MS​=21​ on the magnetic field axis. This is the lowest-energy state of ${}^{2}\ensuremath{\Sigma}$ molecules confined in a magnetic trap. The results are averaged over calculations with multiple molecule-molecule interaction potentials, which yield the expectation intervals for the cross sections and the elastic-to-inelastic cross-section ratios. We find that the elastic-to-inelastic cross-section ratios under conditions corresponding to trapped molecular ensembles at $T\ensuremath{\sim}{10}^{\ensuremath{-}3}$ K exceed 100 for the majority of ${}^{2}\ensuremath{\Sigma}$ molecules. The range of ${}^{2}\ensuremath{\Sigma}$ molecules expected to be collisionally unstable in magnetic traps at $T<{10}^{\ensuremath{-}3}$ K is limited to molecules with the spin-rotation interaction constant ${\ensuremath{\gamma}}_{\mathrm{SR}}>0.5$ cm${}^{\ensuremath{-}1}$ and the rotational constant Be<4{B}_{e}<4Be​<4 cm${}^{\ensuremath{-}1}$.
We present elastic and inelastic spin-changing cross sections for cold and ultracold NH(X (3)Σ(-)) + NH(X (3)Σ(-)) collisions, obtained from full quantum scattering calculations on an accurate ab initio quintet potential-energy surface. Although we consider only collisions in zero field, we focus on the cross sections relevant for magnetic trapping experiments. It is shown that evaporative cooling of both fermionic (14)NH and bosonic (15)NH is likely to be successful for hyperfine states that allow s-wave collisions. The calculated cross sections are very sensitive to the details of the interaction potential, due to the presence of (quasi)bound state resonances. The remaining inaccuracy of the ab initio potential-energy surface therefore gives rise to an uncertainty in the numerical cross-section values. However, based on a sampling of the uncertainty range of the ab initio calculations, we conclude that the exact potential is likely to be such that the elastic-to-inelastic cross-section ratio is sufficiently large to achieve efficient evaporative cooling. This likelihood is only weakly dependent on the size of the channel basis set used in the scattering calculations.
The dynamics of magnetic relaxation of Tm atoms in cold helium gas is investigated using ab initio interaction potentials between Tm(2F)\mathrm{Tm}(^{2}F)Tm(2F) and He atoms. The interaction of Tm(2F)\mathrm{Tm}(^{2}F)Tm(2F) with He gives rise to four adiabatic potentials of ${\ensuremath{\Sigma}}^{+}$, $\ensuremath{\Pi}$, $\ensuremath{\Delta}$, and $\ensuremath{\Phi}$ symmetries, which are found to be degenerate to within $0.1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ at all interatomic distances larger than R=5.4A˚R=5.4\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}R=5.4A˚. The small splitting between the interaction potentials leads to suppression of Zeeman transitions in Tm-He collisions. Our quantum scattering calculations yield a small rate constant of $1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ for Zeeman relaxation of the Tm(2F7∕2)\mathrm{Tm}(^{2}F_{7∕2})Tm(2F7∕2​) atoms in the maximally stretched M=7∕2M=7∕2M=7∕2 sublevel at the temperature 0.8K0.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}0.8K, in reasonable agreement with the measured value $(5.0\ifmmode\pm\else\textpm\fi{}2.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. The sensitivity of Zeeman-relaxation cross sections to details of the interaction potentials is examined. To our knowledge, this is one of only two comparisons of ab initio quantum scattering calculations with experimental measurements of inelastic collisions at subkelvin temperatures near one Kelvin. Our work thus demonstrates the feasibility of describing cold collisions from first principles.
NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with 3He^{3}\mathrm{He}3He is measured to be $3.8\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}\text{ }\text{ }{\mathrm{cm}}^{2}$ at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of $\ensuremath{\gamma}=7\ifmmode\times\else\texttimes\fi{}{10}^{4}$, in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K\l{}os, and G. Cha\l{}asi\ifmmode \acute{n}\else \'{n}\fi{}ski, Phys. Rev. A 68, 051401 (2003)].