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:0804.0265 · Physical Review Letters

Mechanism of Collisional Spin Relaxation in Σ3 Molecules

Wesley C. Campbell, Timur V. Tscherbul, Hsin-I Lu, Edem Tsikata, Roman V. Krems, John M. Doyle

Published Jan 6, 2009• 53 citations
arXivHTMLPDF

Abstract

We measure and theoretically determine the effect of molecular rotational splitting on Zeeman relaxation rates in collisions of cold 3Sigma molecules with helium atoms in a magnetic field. All four stable isotopomers of the imidogen (NH) molecule are magnetically trapped and studied in collisions with 3He and 4He. The 4He data support the predicted 1/B_{e};{2} dependence of the collision-induced Zeeman relaxation rate coefficient on the molecular rotational constant B_{e}. The measured 3He rate coefficients are much larger than the 4He coefficients, depend less strongly on B_{e}, and theoretical analysis indicates they are strongly affected by a shape resonance. The results demonstrate the influence of molecular structure on collisional energy transfer at low temperatures.

DOI
10.1103/physrevlett.102.013003

Related papers

Zeeman Relaxation of CaF in Low-Temperature Collisions with Helium

Kenneth Maussang, Dima Egorov, Joel S. Helton +2 more

The collision-induced Zeeman relaxation rate for collisions of CaF ${X}^{2}\ensuremath{\Sigma}({v}^{\ensuremath{'}\ensuremath{'}}=0)$ with $^{3}\mathrm{He}$ is measured to be ${\ensuremath{\Gamma}}_{\mathrm{Z}}=(7.7+5.4/\ensuremath{-}2.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$ at 2 K. This rate is a direct measurement of the influence of spin-rotation coupling on Zeeman relaxation in the first rotational level of CaF. The relationship of this rate to known molecular constants is consistent with recent theory of cold molecular collisions and outlines the $^{2}\ensuremath{\Sigma}$ molecules conducive to magnetic trapping.

Physical Review Letters•Mar 29, 2005•77 citations

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

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

Roman V. Krems, H. R. Sadeghpour, A. Dalgarno +3 more

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.

Physical Review A•Nov 12, 2003•72 citations

Nuclear Spin Relaxation in Cold Atom–Molecule Collisions

Rebekah Hermsmeier, Xiaodong Xing, Timur V. Tscherbul

We explore the quantum dynamics of nuclear spin relaxation in cold collisions of 1 Σ + molecules with structureless atoms in an external magnetic field. To this end, we develop a rigorous coupled-channel methodology, which accounts for rotational and nuclear spin degrees of freedom of 1 Σ + molecules and their interaction with an external magnetic field as well as anisotropic atom–molecule interactions. We apply the methodology to study the collisional relaxation of the nuclear spin sublevels of 13 CO molecules immersed in a cold buffer gas of 4 He atoms. We find that nuclear spin relaxation in the ground rotational manifold ( N = 0) of 13 CO occurs extremely slowly due to the absence of direct couplings between the nuclear spin sublevels. The rates of collisional transitions between the rotationally excited ( N = 1) nuclear spin states of 13 CO are generally much higher due to the direct nuclear spin–rotation coupling between the states. These transitions obey selection rules, which depend on the values of space-fixed projections of rotational and nuclear spin angular momenta ( M N and M I ) for the initial and final molecular states. For some initial states, we also observe a strong magnetic field dependence, which can be understood by using the first Born approximation. We use our calculated nuclear spin relaxation rates to investigate the thermalization of a single nuclear spin state of 13 CO( N = 0) immersed in a cold buffer gas of 4 He. The calculated nuclear spin relaxation times ( T 1 ≃ 1 s at T = 1 K at a He density of 10 –14 cm –3 ) display a steep temperature dependence decreasing rapidly at elevated temperatures due to the increased population of rotationally excited states, which undergo nuclear spin relaxation at a much faster rate. Thus, long relaxation times of N = 0 nuclear spin states in cold collisions with buffer gas atoms can be maintained only at sufficiently low temperatures ( k B T ≪ 2 B e ), where B e is the rotational constant.

arXiv:2212.05363•The Journal of Physical Chemistry A•May 16, 2023•6 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

Manipulating spin-dependent interactions in rotationally excited cold molecules with electric fields

Timur V. Tscherbul, Roman V. Krems

We use rigorous quantum mechanical theory to study collisions of magnetically oriented cold molecules in the presence of superimposed electric and magnetic fields. It is shown that electric fields suppress the spin-rotation interaction in rotationally excited 2Sigma molecules and inhibit rotationally elastic and inelastic transitions accompanied by electron spin reorientation. We demonstrate that electric fields enhance collisional spin relaxation in 3Sigma molecules and discuss the mechanisms for electric field control of spin-changing transitions in collisions of rotationally excited CaD(2Sigma) and ND(3Sigma) molecules with helium atoms. The propensities for spin depolarization in the rotationally excited molecules are analyzed based on the calculations of collision rate constants at T=0.5 K.

The Journal of Chemical Physics•Nov 16, 2006•42 citations
We measure and theoretically determine the effect of molecular rotational splitting on Zeeman relaxation rates in collisions of cold 3Sigma molecules with helium atoms in a magnetic field. All four stable isotopomers of the imidogen (NH) molecule are magnetically trapped and studied in collisions with 3He and 4He. The 4He data support the predicted 1/B_{e};{2} dependence of the collision-induced Zeeman relaxation rate coefficient on the molecular rotational constant B_{e}. The measured 3He rate coefficients are much larger than the 4He coefficients, depend less strongly on B_{e}, and theoretical analysis indicates they are strongly affected by a shape resonance. The results demonstrate the influence of molecular structure on collisional energy transfer at low temperatures.
The collision-induced Zeeman relaxation rate for collisions of CaF ${X}^{2}\ensuremath{\Sigma}({v}^{\ensuremath{'}\ensuremath{'}}=0)$ with 3He^{3}\mathrm{He}3He is measured to be ${\ensuremath{\Gamma}}_{\mathrm{Z}}=(7.7+5.4/\ensuremath{-}2.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\text{ }{\mathrm{cm}}^{3}/\mathrm{s}$ at 2 K. This rate is a direct measurement of the influence of spin-rotation coupling on Zeeman relaxation in the first rotational level of CaF. The relationship of this rate to known molecular constants is consistent with recent theory of cold molecular collisions and outlines the $^{2}\ensuremath{\Sigma}$ molecules conducive to magnetic trapping.
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%.
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 3He{}^{3}\mathrm{He}3He 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-3He{}^{3}\mathrm{He}3He collisions exceeds 105{10}^{5}105 at temperatures between 0.50.50.5 and 1 K.
We explore the quantum dynamics of nuclear spin relaxation in cold collisions of 1 Σ + molecules with structureless atoms in an external magnetic field. To this end, we develop a rigorous coupled-channel methodology, which accounts for rotational and nuclear spin degrees of freedom of 1 Σ + molecules and their interaction with an external magnetic field as well as anisotropic atom–molecule interactions. We apply the methodology to study the collisional relaxation of the nuclear spin sublevels of 13 CO molecules immersed in a cold buffer gas of 4 He atoms. We find that nuclear spin relaxation in the ground rotational manifold ( N = 0) of 13 CO occurs extremely slowly due to the absence of direct couplings between the nuclear spin sublevels. The rates of collisional transitions between the rotationally excited ( N = 1) nuclear spin states of 13 CO are generally much higher due to the direct nuclear spin–rotation coupling between the states. These transitions obey selection rules, which depend on the values of space-fixed projections of rotational and nuclear spin angular momenta ( M N and M I ) for the initial and final molecular states. For some initial states, we also observe a strong magnetic field dependence, which can be understood by using the first Born approximation. We use our calculated nuclear spin relaxation rates to investigate the thermalization of a single nuclear spin state of 13 CO( N = 0) immersed in a cold buffer gas of 4 He. The calculated nuclear spin relaxation times ( T 1 ≃ 1 s at T = 1 K at a He density of 10 –14 cm –3 ) display a steep temperature dependence decreasing rapidly at elevated temperatures due to the increased population of rotationally excited states, which undergo nuclear spin relaxation at a much faster rate. Thus, long relaxation times of N = 0 nuclear spin states in cold collisions with buffer gas atoms can be maintained only at sufficiently low temperatures ( k B T ≪ 2 B e ), where B e is the rotational constant.
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)].
We use rigorous quantum mechanical theory to study collisions of magnetically oriented cold molecules in the presence of superimposed electric and magnetic fields. It is shown that electric fields suppress the spin-rotation interaction in rotationally excited 2Sigma molecules and inhibit rotationally elastic and inelastic transitions accompanied by electron spin reorientation. We demonstrate that electric fields enhance collisional spin relaxation in 3Sigma molecules and discuss the mechanisms for electric field control of spin-changing transitions in collisions of rotationally excited CaD(2Sigma) and ND(3Sigma) molecules with helium atoms. The propensities for spin depolarization in the rotationally excited molecules are analyzed based on the calculations of collision rate constants at T=0.5 K.