Formation and dynamics of van der Waals molecules in buffer-gas traps

Nathan Brahms, Timur V. Tscherbul, Peng Zhang, Jacek Kłos, Robert C. Forrey, Yat Shan Au, H. R. Sadeghpour, A. Dalgarno, John M. Doyle, Thad G. Walker

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, 3He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag3He, and report on our spectroscopic search for Ag 3He, which produced a null result.

Original languageEnglish (US)
Pages (from-to)19125-19141
Number of pages17
JournalPhysical Chemistry Chemical Physics
Volume13
Issue number42
DOIs
StatePublished - Nov 14 2011

Fingerprint

Buffers
buffers
Gases
traps
Molecules
Atoms
gases
molecules
Helium
atoms
gas cooling
interactions
helium atoms
chemical equilibrium
Thermodynamics
Scattering
Cooling
dissociation
life (durability)
thermodynamics

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Brahms, N., Tscherbul, T. V., Zhang, P., Kłos, J., Forrey, R. C., Au, Y. S., ... Walker, T. G. (2011). Formation and dynamics of van der Waals molecules in buffer-gas traps. Physical Chemistry Chemical Physics, 13(42), 19125-19141. https://doi.org/10.1039/c1cp21317b
Brahms, Nathan ; Tscherbul, Timur V. ; Zhang, Peng ; Kłos, Jacek ; Forrey, Robert C. ; Au, Yat Shan ; Sadeghpour, H. R. ; Dalgarno, A. ; Doyle, John M. ; Walker, Thad G. / Formation and dynamics of van der Waals molecules in buffer-gas traps. In: Physical Chemistry Chemical Physics. 2011 ; Vol. 13, No. 42. pp. 19125-19141.
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Brahms, N, Tscherbul, TV, Zhang, P, Kłos, J, Forrey, RC, Au, YS, Sadeghpour, HR, Dalgarno, A, Doyle, JM & Walker, TG 2011, 'Formation and dynamics of van der Waals molecules in buffer-gas traps', Physical Chemistry Chemical Physics, vol. 13, no. 42, pp. 19125-19141. https://doi.org/10.1039/c1cp21317b

Formation and dynamics of van der Waals molecules in buffer-gas traps. / Brahms, Nathan; Tscherbul, Timur V.; Zhang, Peng; Kłos, Jacek; Forrey, Robert C.; Au, Yat Shan; Sadeghpour, H. R.; Dalgarno, A.; Doyle, John M.; Walker, Thad G.

In: Physical Chemistry Chemical Physics, Vol. 13, No. 42, 14.11.2011, p. 19125-19141.

Research output: Contribution to journalArticle

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T1 - Formation and dynamics of van der Waals molecules in buffer-gas traps

AU - Brahms, Nathan

AU - Tscherbul, Timur V.

AU - Zhang, Peng

AU - Kłos, Jacek

AU - Forrey, Robert C.

AU - Au, Yat Shan

AU - Sadeghpour, H. R.

AU - Dalgarno, A.

AU - Doyle, John M.

AU - Walker, Thad G.

PY - 2011/11/14

Y1 - 2011/11/14

N2 - We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, 3He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag3He, and report on our spectroscopic search for Ag 3He, which produced a null result.

AB - We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, 3He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag3He, and report on our spectroscopic search for Ag 3He, which produced a null result.

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