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Morita M, Brumer P, Tscherbul TV. Multichannel Quantum Defect Theory with a Frame Transformation for Ultracold Atom-Molecule Collisions in Magnetic Fields. PHYSICAL REVIEW LETTERS 2024; 133:093402. [PMID: 39270161 DOI: 10.1103/physrevlett.133.093402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2023] [Revised: 04/13/2024] [Accepted: 07/11/2024] [Indexed: 09/15/2024]
Abstract
We extend the powerful formalism of multichannel quantum defect theory combined with a frame transformation to ultracold atom-molecule collisions in magnetic fields. By solving the coupled-channel equations with hyperfine and Zeeman interactions omitted at short range, the extended theory enables a drastically simplified description of the intricate quantum dynamics of ultracold molecular collisions in terms of a small number of short-range parameters. We apply the formalism to ultracold Mg+NH collisions in a magnetic field, achieving a 10^{4}-fold reduction in computational effort.
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Affiliation(s)
- Masato Morita
- Chemical Physics Theory Group, Department of Chemistry, and Center for Quantum Information and Quantum Control, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Paul Brumer
- Chemical Physics Theory Group, Department of Chemistry, and Center for Quantum Information and Quantum Control, University of Toronto, Toronto, Ontario M5S 3H6, Canada
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Koyu S, Hermsmeier R, Tscherbul TV. Total angular momentum representation for state-to-state quantum scattering of cold molecules in a magnetic field. J Chem Phys 2022; 156:034112. [DOI: 10.1063/5.0074844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Suyesh Koyu
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
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Morita M, Tscherbul TV. Restricted basis set coupled-channel calculations on atom-molecule collisions in magnetic fields. J Chem Phys 2019; 150:074110. [PMID: 30795668 DOI: 10.1063/1.5047063] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Rigorous coupled-channel quantum scattering calculations on molecular collisions in external fields are computationally demanding due to the need to account for a large number of coupled channels and multiple total angular momenta J of the collision complex. We show that by restricting the total angular momentum basis to include only the states with helicities K ≤ Kmax, it is possible to obtain accurate elastic and inelastic cross sections for low-temperature He + CaH, Li + CaH, and Li + SrOH collisions in the presence of an external magnetic field at a small fraction of the computational cost of the full coupled-channel calculations (where K is the projection of the molecular rotational angular momentum on the atom-diatom axis). The optimal size of the truncated helicity basis set depends on the mechanism of the inelastic process and on the magnitude of the external magnetic field, with the minimal basis set (Kmax = 0) producing quantitatively accurate results for, e.g., ultracold Li + CaH and Li + SrOH scattering at low magnetic fields, leading to nearly 90-fold gain in computational efficiency. Larger basis sets are required to accurately describe the resonance structure in the magnetic field dependence of Li + CaH and Li + SrOH inelastic cross sections in the few partial wave-regime as well as indirect spin relaxation in He + CaH collisions. Our calculations indicate that the resonance structure is due to an interplay of the spin-rotation and Coriolis couplings between the basis states of different K and the couplings between the rotational states of the same K induced by the anisotropy of the interaction potential.
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Affiliation(s)
- Masato Morita
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
| | - Timur V Tscherbul
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
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Vieira D, Krems RV, Tscherbul TV. Molecular collisions and reactive scattering in external fields: Are field-induced couplings important at short range? J Chem Phys 2017; 146:024102. [PMID: 28088162 DOI: 10.1063/1.4973431] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We use accurate quantum scattering calculations to elucidate the role of short-range molecule-field interactions in atom-molecule inelastic collisions and abstraction chemical reactions at low temperatures. We consider two examples: elastic and inelastic scattering of NH(Σ3) molecules with Mg(S1) atoms in a magnetic field; reactive scattering LiF + H → Li + HF in an electric field. Our calculations suggest that, for non-reactive collision systems and abstraction chemical reactions, the molecule-field interactions cannot generally be neglected at short range because the atom-molecule potential passes through zero at short range. An important exception occurs for Zeeman transitions in atom-molecule collisions at magnetic fields ≲1000 G, for which the molecule-field couplings need only be included at large ρ outside the range of the atom-molecule interaction. Our results highlight the importance of an accurate description of ρ-dependent molecule-field interactions in quantum scattering calculations on molecular collisions and chemical reactions at low temperatures.
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Affiliation(s)
- D Vieira
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - R V Krems
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - T V Tscherbul
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
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Balakrishnan N. Perspective: Ultracold molecules and the dawn of cold controlled chemistry. J Chem Phys 2016; 145:150901. [DOI: 10.1063/1.4964096] [Citation(s) in RCA: 157] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- N. Balakrishnan
- Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154, USA
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Cui J, Krems RV. Gaussian Process Model for Collision Dynamics of Complex Molecules. PHYSICAL REVIEW LETTERS 2015; 115:073202. [PMID: 26317721 DOI: 10.1103/physrevlett.115.073202] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Indexed: 06/04/2023]
Abstract
We show that a Gaussian process model can be combined with a small number (of order 100) of scattering calculations to provide a multidimensional dependence of scattering observables on the experimentally controllable parameters (such as the collision energy or temperature) as well as the potential energy surface (PES) parameters. For the case of Ar-C_{6}H_{6} collisions, we show that 200 classical trajectory calculations are sufficient to provide a ten-dimensional hypersurface, giving the dependence of the collision lifetimes on the collision energy, internal temperature, and eight PES parameters. This can be used for solving the inverse scattering problem, for the efficient calculation of thermally averaged observables, for reducing the error of the molecular dynamics calculations by averaging over the PES variations, and for the analysis of the sensitivity of the observables to individual parameters determining the PES. Trained by a combination of classical and quantum calculations, the model provides an accurate description of the quantum scattering cross sections, even near scattering resonances.
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Affiliation(s)
- Jie Cui
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - Roman V Krems
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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Abstract
Over the past decade, and particularly the past five years, a quiet revolution has been building at the border between atomic physics and experimental quantum chemistry. The rapid development of techniques for producing cold and even ultracold molecules without a perturbing rare-gas cluster shell is now enabling the study of chemical reactions and scattering at the quantum scattering limit with only a few partial waves contributing to the incident channel. Moreover, the ability to perform these experiments with nonthermal distributions comprising one or a few specific states enables the observation and even full control of state-to-state collision rates in this computation-friendly regime: This is perhaps the most elementary study possible of scattering and reaction dynamics.
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Affiliation(s)
- Benjamin K Stuhl
- Joint Quantum Institute, National Institute of Standards and Technology and University of Maryland, Gaithersburg, Maryland 20899
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Affiliation(s)
- Mikhail Lemeshko
- a ITAMP, Harvard-Smithsonian Center for Astrophysics , Cambridge , MA , 02138 , USA
- b Physics Department , Harvard University , Cambridge , MA , 02138 , USA
- c Kavli Institute for Theoretical Physics , University of California , Santa Barbara , CA , 93106 , USA
| | - Roman V. Krems
- c Kavli Institute for Theoretical Physics , University of California , Santa Barbara , CA , 93106 , USA
- d Department of Chemistry , University of British Columbia , BC V6T 1Z1, Vancouver , Canada
| | - John M. Doyle
- b Physics Department , Harvard University , Cambridge , MA , 02138 , USA
| | - Sabre Kais
- e Departments of Chemistry and Physics , Purdue University , West Lafayette , IN , 47907 , USA
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Janssen LMC, van der Avoird A, Groenenboom GC. Quantum reactive scattering of ultracold NH(X (3)Σ(-)) radicals in a magnetic trap. PHYSICAL REVIEW LETTERS 2013; 110:063201. [PMID: 23432241 DOI: 10.1103/physrevlett.110.063201] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Indexed: 06/01/2023]
Abstract
We investigate the ultracold reaction dynamics of magnetically trapped NH(X (3)Σ(-)) radicals using rigorous quantum scattering calculations involving three coupled potential energy surfaces. We find that the reactive NH+NH cross section is driven by a short-ranged collisional mechanism, and its magnitude is only weakly dependent on magnetic field strength. Unlike most ultracold reactions observed so far, the NH+NH scattering dynamics is nonuniversal. Our results indicate that chemical reactions can cause more trap loss than spin-inelastic NH+NH collisions, making molecular evaporative cooling more difficult than previously anticipated.
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Affiliation(s)
- Liesbeth M C Janssen
- Radboud University Nijmegen, Institute for Molecules and Materials, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
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Stuhl BK, Hummon MT, Yeo M, Quéméner G, Bohn JL, Ye J. Evaporative cooling of the dipolar hydroxyl radical. Nature 2012; 492:396-400. [DOI: 10.1038/nature11718] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2012] [Accepted: 10/26/2012] [Indexed: 12/12/2022]
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