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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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Pawlak M, Żuchowski PS, Moiseyev N, Jankowski P. Evidence of Nonrigidity Effects in the Description of Low-Energy Anisotropic Molecular Collisions of Hydrogen Molecules with Excited Metastable Helium Atoms. J Chem Theory Comput 2020; 16:2450-2459. [PMID: 32150402 PMCID: PMC7497643 DOI: 10.1021/acs.jctc.0c00183] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Cold collisions serve
as a sensitive probe of the interaction potential.
In the recent study of Klein et al. (Nature Phys.2017, 13, 35–38), the one-parameter
scaling of the interaction potential was necessary to obtain agreement
between theoretical and observed patterns of the orbiting resonances
for excited metastable helium atoms colliding with hydrogen molecules.
Here, we show that the effect of nonrigidity of the H2 molecule
on the resonant structure, absent in the previous study, is critical
to predict the correct positions of the resonances in that case. We
have complemented the theoretical description of the interaction potential
and revised reaction rate coefficients by proper inclusion of the
flexibility of the molecule. The calculated reaction rate coefficients
are in remarkable agreement with the experimental data without empirical
adjustment of the interaction potential. We have shown that even state-of-the-art
calculations of the interaction energy cannot ensure agreement with
the experiment if such an important physical effect as flexibility
of the interacting molecule is neglected. Our findings about the significance
of the nonrigidity effects can be especially crucial in cold chemistry,
where the quantum nature of molecules is pronounced.
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Affiliation(s)
- Mariusz Pawlak
- Faculty of Chemistry, Nicolaus Copernicus University in Toruń, Gagarina 7, 87-100 Toruń, Poland
| | - Piotr S Żuchowski
- Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, Grudziądzka 5, 87-100 Toruń, Poland
| | - Nimrod Moiseyev
- Schulich Faculty of Chemistry and Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Piotr Jankowski
- Faculty of Chemistry, Nicolaus Copernicus University in Toruń, Gagarina 7, 87-100 Toruń, Poland
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3
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Yang B, Zhang P, Qu C, Stancil P, Bowman J, Balakrishnan N, Forrey R. Full-dimensional quantum dynamics of SO(X3Σ-) in collision with H2. Chem Phys 2020. [DOI: 10.1016/j.chemphys.2020.110695] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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4
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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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5
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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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6
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Babikov D, Semenov A. Recent Advances in Development and Applications of the Mixed Quantum/Classical Theory for Inelastic Scattering. J Phys Chem A 2015; 120:319-31. [DOI: 10.1021/acs.jpca.5b09569] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Dmitri Babikov
- Chemistry
Department, Wehr
Chemistry Building, Marquette University, Milwaukee, Wisconsin 53201-1881, United States
| | - Alexander Semenov
- Chemistry
Department, Wehr
Chemistry Building, Marquette University, Milwaukee, Wisconsin 53201-1881, United States
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Semenov A, Babikov D. Mixed Quantum/Classical Theory for Molecule–Molecule Inelastic Scattering: Derivations of Equations and Application to N2 + H2 System. J Phys Chem A 2015; 119:12329-38. [DOI: 10.1021/acs.jpca.5b06812] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Alexander Semenov
- Chemistry
Department, Wehr Chemistry Building, Marquette University, Milwaukee, Wisconsin 53201-1881, United States
| | - Dmitri Babikov
- Chemistry
Department, Wehr Chemistry Building, Marquette University, Milwaukee, Wisconsin 53201-1881, United States
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8
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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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9
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Singh V, Hardman KS, Lu MJ, Ellis A, Morrison MJ, Weinstein JD. Inelastic collisions of CaH with He at cryogenic temperatures. Mol Phys 2013. [DOI: 10.1080/00268976.2013.772668] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Vijay Singh
- a Department of Physics , University of Nevada , Reno , USA
| | | | - Mei-Ju Lu
- a Department of Physics , University of Nevada , Reno , USA
| | - Aja Ellis
- a Department of Physics , University of Nevada , Reno , USA
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10
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Singh V, Hardman KS, Tariq N, Lu MJ, Ellis A, Morrison MJ, Weinstein JD. Chemical reactions of atomic lithium and molecular calcium monohydride at 1 K. PHYSICAL REVIEW LETTERS 2012; 108:203201. [PMID: 23003146 DOI: 10.1103/physrevlett.108.203201] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2012] [Indexed: 06/01/2023]
Abstract
Using cryogenic helium buffer-gas cooling, we have prepared dense samples of atomic lithium and molecular calcium monohydride at temperatures as low as 1 K. We have measured the Li+CaH→LiH+Ca chemical reaction, observed in both the accelerated disappearance of CaH in the presence of high densities of lithium and in the appearance of the LiH molecule.
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Affiliation(s)
- Vijay Singh
- Department of Physics, University of Nevada, Reno, Nevada 89557, USA
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11
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Guillon G, Viel A, Launay JM. Full dimension Rb2He ground triplet potential energy surface and quantum scattering calculations. J Chem Phys 2012; 136:174307. [DOI: 10.1063/1.4709433] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
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12
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García-Vela A, Cabanillas-Vidosa I, Ferrero JC, Pino GA. The role of orbiting resonances in the vibrational relaxation of I(2)(B,v' = 21) by collisions with He at very low energies: a theoretical and experimental study. Phys Chem Chem Phys 2012; 14:5570-80. [PMID: 22434127 DOI: 10.1039/c2cp24061k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The low-energy collisions of I(2)(B,v' = 21) with He involving collision-induced vibrational relaxation of I(2) are investigated both experimentally and by means of wave packet simulations. The theoretical cross sections exhibit a structure of peaks originated by orbiting resonances of the I(2)(B,v' = 21) - He van der Waals complex formed in the I(2) + He collisions. Such a structure has similar characteristics as the structure of peaks found in the experimental cross sections. In fact, four of the five peaks of the measured cross sections appear at positions nearly coincident with those of four of the peaks found in the theoretical cross sections. Thus this result confirms the experimental finding that enhancement of I(2) vibrational relaxation is caused by the population of I(2)(B,v' = 21) - He orbiting resonances populated upon the low-energy collisions. The possibility of using this mechanism in the vibrational cooling of diatomic molecules is discussed.
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Affiliation(s)
- Alberto García-Vela
- Instituto de Física Fundamental, C.S.I.C., Serrano 123, 28006 Madrid, Spain.
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13
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14
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15
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Feng E, Shao X, Yu C, Sun C, Huang W. Low energy collisions of CN(X 2Σ+) with He in magnetic fields. J Chem Phys 2012; 136:054302. [DOI: 10.1063/1.3679869] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Eryin Feng
- Department of Physics, Anhui normal university, Wuhu 241000, People's Republic of China
| | - Xi Shao
- Department of Physics, Anhui normal university, Wuhu 241000, People's Republic of China
| | - Chunhua Yu
- Department of Physics, Anhui normal university, Wuhu 241000, People's Republic of China
| | - Chunyan Sun
- Department of Physics, Anhui normal university, Wuhu 241000, People's Republic of China
| | - Wuying Huang
- Department of Physics, Anhui normal university, Wuhu 241000, People's Republic of China
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16
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Tscherbul TV, Sayfutyarova ER, Buchachenko AA, Dalgarno A. He–ThO(1Σ+) interactions at low temperatures: Elastic and inelastic collisions, transport properties, and complex formation in cold4He gas. J Chem Phys 2011; 134:144301. [DOI: 10.1063/1.3575399] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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17
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18
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Chandler DW. Cold and ultracold molecules: Spotlight on orbiting resonances. J Chem Phys 2010; 132:110901. [DOI: 10.1063/1.3357286] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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19
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Lique F, Kłos J, Hochlaf M. Benchmarks for the generation of interaction potentials for scattering calculations: applications to rotationally inelastic collisions of C4 (X3Σ−g) with He. Phys Chem Chem Phys 2010; 12:15672-80. [DOI: 10.1039/c004945j] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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20
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Janssen LMC, Groenenboom GC, van der Avoird A, Żuchowski PS, Podeszwa R. Ab initio potential energy surfaces for NH(Σ3−)–NH(Σ3−) with analytical long range. J Chem Phys 2009; 131:224314. [DOI: 10.1063/1.3268920] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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21
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Tscherbul TV. Differential scattering of cold molecules in superimposed electric and magnetic fields. J Chem Phys 2008; 128:244305. [DOI: 10.1063/1.2943197] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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22
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Abrahamsson E, Tscherbul TV, Krems RV. Inelastic collisions of cold polar molecules in nonparallel electric and magnetic fields. J Chem Phys 2007; 127:044302. [PMID: 17672685 DOI: 10.1063/1.2748770] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The authors present a detailed study of low-temperature collisions between CaD molecules and He atoms in superimposed electric and magnetic fields with arbitrary orientations. Electric fields do not interact with the electron spin of the molecules directly but modify their rotational structure and, consequently, the spin-rotation interactions. The authors examine molecular Stark and Zeeman energy levels as functions of the angle between the fields and show that rotating fields may induce and shift avoided crossings between the Zeeman levels of the rotationally ground and rotationally excited states of the molecule. The dynamics of molecular collisions are extremely sensitive to external fields near these avoided crossings and it is shown that molecular collisions may be controlled by varying both the strength and the relative orientation of the fields. The effects observed in this study are due to interactions of the isolated molecules with external fields so the conclusions should be relevant for collisions of molecules with other atoms or collisions of molecules with each other. This study demonstrates that electric fields may be used to enhance or suppress spin-rotation interactions in molecules. The spin-rotation interactions induce nonadiabatic couplings between states of different total spins in systems of two open-shell species and it is suggested that electric fields might be used for controlling nonadiabatic spin transitions and spin-forbidden chemical reactions of cold molecules in a magnetic trap.
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Affiliation(s)
- E Abrahamsson
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
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23
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Weck PF, Balakrishnan N, Brandão J, Rosa C, Wang W. Dynamics of the O(3P) + H2 reaction at low temperatures: comparison of quasiclassical trajectory with quantum scattering calculations. J Chem Phys 2007; 124:74308. [PMID: 16497037 DOI: 10.1063/1.2172239] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Quasiclassical trajectory and quantum-mechanical scattering calculations are reported for the O((3)P) + H(2)(X (1)Sigma(g) (+);upsilon = 1-3,j = 0)-->OH(X (2)Pi) + H((2)S) reaction at energies close to the reaction threshold. The dynamics of the reaction have been investigated for zero total angular momentum using the lowest (3)A" potential-energy surface developed by Rogers et al. [J. Phys. Chem. A 104, 2308 (2000)] and its recent extensions by Brandao et al. [J. Chem. Phys. 121, 8861 (2004)] which provide an improved description of the van der Waals interaction. Good agreement is observed for this system between quasiclassical and quantal results for incident kinetic energies above the tunneling regime. Quantum-mechanical calculations also confirm recent theoretical predictions of a strong collision-energy dependence of the OH(v(') = 0)OH(v' = 1) product branching ratio in the O((3)P) + H(2)(v = 1) reaction, which explains the differences observed in OH vibrational populations between experiments using different O((3)P) sources.
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Affiliation(s)
- P F Weck
- Department of Chemistry, University of Nevada Las Vegas, 89154, USA.
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24
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Tscherbul TV, Krems RV. Manipulating spin-dependent interactions in rotationally excited cold molecules with electric fields. J Chem Phys 2006; 125:194311. [PMID: 17129107 DOI: 10.1063/1.2374896] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
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.
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Affiliation(s)
- T V Tscherbul
- Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
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25
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Tscherbul TV, Krems RV. Controlling electronic spin relaxation of cold molecules with electric fields. PHYSICAL REVIEW LETTERS 2006; 97:083201. [PMID: 17026301 DOI: 10.1103/physrevlett.97.083201] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2006] [Indexed: 05/12/2023]
Abstract
We present a theoretical study of atom-molecule collisions in superimposed electric and magnetic fields and show that dynamics of electronic spin relaxation in molecules at temperatures below 0.5 K can be manipulated by varying the strength and the relative orientation of the applied fields. The mechanism of electric field control of Zeeman transitions is based on an intricate interplay between intramolecular spin-rotation couplings and molecule-field interactions. We suggest that electric fields may affect chemical reactions through inducing nonadiabatic spin transitions and facilitate evaporative cooling of molecules in a magnetic trap.
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Affiliation(s)
- T V Tscherbul
- Department of Chemistry, University of British Columbia, Vancouver, B.C. V6T 1Z1, Canada
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26
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Weck PF, Balakrishnan N. Importance of long-range interactions in chemical reactions at cold and ultracold temperatures. INT REV PHYS CHEM 2006. [DOI: 10.1080/01442350600791894] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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27
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Bodo E, Gianturco FA. Collisional quenching of molecular ro-vibrational energy by He buffer loading at ultralow energies. INT REV PHYS CHEM 2006. [DOI: 10.1080/01442350600772928] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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28
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Weck PF, Balakrishnan N. Reactivity enhancement of ultracold O(P3)+H2 collisions by van der Waals interactions. J Chem Phys 2005; 123:144308. [PMID: 16238392 DOI: 10.1063/1.2060710] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The role of van der Waals forces in O((3)P)+H(2)(upsilon=1,j=0) collisions is investigated theoretically at low and ultralow temperatures. Quantum scattering calculations have been performed for zero total angular momentum using the lowest London-Eyring-Polanyi-Sato double-polynomial (3)A(") potential-energy surface reported by [Rogers et al., J. Phys. Chem. A 104, 2308 (2000)] and its recent BMS1 and BMS2 extensions developed by [Brandao et al., J. Chem. Phys. 121, 8861 (2004)] which provide a more accurate treatment of the van der Waals interaction. Our calculations show that van der Waals forces strongly influence chemical reactivity at ultracold translational energies. The presence of a zero-energy resonance for the BMS1 surface is found to enhance reactivity in the ultracold regime and shift the Wigner threshold to lower temperatures.
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Affiliation(s)
- P F Weck
- Department of Chemistry, University of Nevada, Las Vegas, Nevada 89154, USA.
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29
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Ronningen TJ, De Lucia FC. Helium induced pressure broadening and shifting of HCN hyperfine transitions between 1.3 and 20 K. J Chem Phys 2005; 122:184319. [PMID: 15918716 DOI: 10.1063/1.1895905] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have measured the helium induced pressure broadening and shifting of the distinct hyperfine components of the j = 1 <-- 0 and j = 2 <-- 1 transitions of HC14N at temperatures between 1.3 and 20 K. The HCN molecules were cooled to these temperatures using the collisional cooling technique. As a test of this cooling technique we measured the Doppler contribution to the spectral lines, and these measurements confirm that the molecules are at the same temperature as the walls of the spectroscopic cell. We observed that the hyperfine components of the 2 <-- 1 transition have distinct broadening coefficients that differ from one another by as much as 5%. The measured differences are in reasonable agreement with theoretical predictions. We have also performed molecular scattering calculations on three He-HCN potential energy surfaces in order to compare our results with theoretical expectations. At the lowest temperatures these calculations predict broadening coefficients that are considerably larger than the measured coefficients. We have previously found a similar discrepancy for two other molecules at these low temperatures, and we discuss possible experimental and theoretical origins for this persistent discrepancy.
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Weck PF, Balakrishnan N. Quantum dynamics of the Li+HF→H+LiF reaction at ultralow temperatures. J Chem Phys 2005; 122:154309. [PMID: 15945637 DOI: 10.1063/1.1884115] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Quantum-mechanical calculations are reported for the Li+HF(v=0,1,j=0)-->H+LiF(v',j') bimolecular scattering process at low and ultralow temperatures. Calculations have been performed for zero total angular momentum using a recent high-accuracy potential-energy surface for the X2A' electronic ground state. For Li+HF(v=0,j=0), the reaction is dominated by resonances due to the decay of metastable states of the Li cdots,...F-H van der Waals complex. Assignment of these resonances has been carried out by calculating the eigenenergies of the quasibound states. We also find that while chemical reactivity is greatly enhanced by vibrational excitation, the resonances get mostly washed out in the reaction of vibrationally excited HF with Li atoms. In addition, we find that at low energies, the reaction is significantly suppressed due to the less-efficient tunneling of the relatively heavy fluorine atom.
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Affiliation(s)
- P F Weck
- Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, USA.
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31
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Maussang K, Egorov D, Helton JS, Nguyen SV, Doyle JM. Zeeman relaxation of CaF in low-temperature collisions with helium. PHYSICAL REVIEW LETTERS 2005; 94:123002. [PMID: 15903915 DOI: 10.1103/physrevlett.94.123002] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2004] [Indexed: 05/02/2023]
Abstract
The collision-induced Zeeman relaxation rate for collisions of CaF X2Sigma(v('')=0) with 3He is measured to be Gamma(Z)=(7.7+5.4/-2.5)x10(-15) cm(3)/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)Sigma molecules conducive to magnetic trapping.
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Affiliation(s)
- Kenneth Maussang
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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32
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Uudus N, Magaki S, Balakrishnan N. Quantum mechanical investigation of rovibrational relaxation of H2 and D2 by collisions with Ar atoms. J Chem Phys 2005; 122:024304. [PMID: 15638583 DOI: 10.1063/1.1829976] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report quantum mechanical calculations of cross sections and rate coefficients for rovibrational relaxation of H2 and D2 by collisions with Ar atoms over a wide range of temperatures including the ultracold limit. Limiting values of the rate coefficients for vibrational and rotational quenching at zero temperature were computed and sensitivity of the results to the choice of the interaction potential is investigated. We also demonstrate dramatic change in the behavior of the rate coefficients at low temperatures when the van der Waals potential supports a quasibound level very close to the dissociation threshold.
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Affiliation(s)
- Nyamsuren Uudus
- Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, USA
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Lee TG, Rochow C, Martin R, Clark TK, Forrey RC, Balakrishnan N, Stancil PC, Schultz DR, Dalgarno A, Ferland GJ. Close-coupling calculations of low-energy inelastic and elastic processes in 4He collisions with H2: A comparative study of two potential energy surfaces. J Chem Phys 2005; 122:024307. [PMID: 15638586 DOI: 10.1063/1.1833351] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The two most recently published potential energy surfaces (PESs) for the HeH2 complex, the so-called MR (Muchnick and Russek) and BMP (Boothroyd, Martin, and Peterson) surfaces, are quantitatively evaluated and compared through the investigation of atom-diatom collision processes. The BMP surface is expected to be an improvement, approaching chemical accuracy, over all conformations of the PES compared to that of the MR surface. We found significant differences in inelastic rovibrational cross sections computed on the two surfaces for processes dominated by large changes in target rotational angular momentum. In particular, the H2(nu=1,j=0) total quenching cross section computed using the BMP potential was found to be a factor of 1000 larger than that obtained with the MR surface. A lesser discrepancy persists over a large range of energies from the ultracold to thermal and occurs for other low-lying initial rovibrational levels. The MR surface was used in previous calculations of the H2(nu=1,j=0) quenching rate coefficient and gave results in close agreement with the experimental data of Audibert et al. which were obtained for temperatures between 50 and 300 K. Examination of the rovibronic coupling matrix elements, which are obtained following a Legendre expansion of the PES, suggests that the magnitude of the anisotropy of the BMP potential is too large in the interaction region. However, cross sections for elastic and pure rotational processes obtained from the two PESs differ typically by less than a factor of 2. The small differences may be ascribed to the long-range and anharmonic components of the PESs. Exceptions occur for (nu=10,j=0) and (nu=11,j=1) where significant enhancements have been found for the low-energy quenching and elastic cross sections due to zero-energy resonances in the BMP PES which are not present in the MR potential.
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Affiliation(s)
- Teck-Ghee Lee
- Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA
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Krems RV. Molecules near absolute zero and external field control of atomic and molecular dynamics. INT REV PHYS CHEM 2005. [DOI: 10.1080/01442350500167161] [Citation(s) in RCA: 220] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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35
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Balakrishnan N. On the role of van der Waals interaction in chemical reactions at low temperatures. J Chem Phys 2004; 121:5563-6. [PMID: 15366978 DOI: 10.1063/1.1799571] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
It is shown that van der Waals interaction potential plays a crucial role in chemical reactions at low temperatures. By taking the Cl+HD reaction as an illustrative example, we demonstrate that quasibound states of the van der Waals potential preferentially undergo chemical reaction rather than vibrational predissociation. Prereaction occurs even when the wave functions of the quasibound states peak far out into the entrance channel, outside the region of the van der Waals well. It is found that chemical reaction dominates over nonreactive vibrational quenching in collisions of vibrationally excited HD molecules with ground state chlorine atoms at ultracold temperatures.
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Affiliation(s)
- N Balakrishnan
- Department of Chemistry, University of Nevada Las Vegas, Las Vegas, Nevada 89154, USA.
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36
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Steimle TC, Chen J, Gengler J. The permanent electric dipole moments of calcium monohydride, CaH. J Chem Phys 2004; 121:829-34. [PMID: 15260612 DOI: 10.1063/1.1759314] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Numerous branch features in the (0,0) A 2Pi-X 2Sigma+ band system of calcium monohydride CaH have been studied by optical Stark spectroscopy. The Stark shifts, Stark splittings, and appearance of electric-field-induced transitions in the high resolution laser-induced fluorescence spectra are analyzed to produce values for the magnitude of the permanent electric dipole moments mid R:micromid R: of 2.94(16) D and 2.372(12) D for the X 2Sigma+(v=0) and A 2Pi(v=0) states, respectively. A comparison with values predicted from a semiempirical electrostatic model and previous ab initio calculations for mid R:micromid R: (X 2Sigma+) is presented. The change in mid R:micromid R: upon excitation from the X 2Sigma+ state to the A 2Pi state is rationalized using a simple molecular orbital description.
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Affiliation(s)
- T C Steimle
- Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604. USA.
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Steimle TC, Gengler J, Chen J. A study of the A2Π/B2Σ+ X2Σ+ band systems of calcium monohydride (CaH) using a supersonic molecular beam source and laser-induced fluorescence detection. CAN J CHEM 2004. [DOI: 10.1139/v04-077] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The high-resolution laser-induced fluorescence spectrum of a molecular beam sample of calcium monohydride (CaH) in the region of the strongly overlapped (1,0) A2Π X2Σ+ and (0,0) B2Σ+ X2Σ+ band systems near 630 nm and the (0,0) A2Π X2Σ+ band system near 690 nm have been recorded and analyzed. The spectral features exhibit a small splitting that is attributed to proton magnetic hyperfine interaction in the X2Σ+ (v = 0) state. The energy levels of the A2Π(v = 0) vibronic state were modeled using a traditional "effective" Hamiltonian approach, whereas those for the interacting A2Π(v = 1)/B2Σ+(v = 0) vibronic levels were modeled by augmenting the traditional effective Hamiltonian with terms to account for local perturbations. An interpretation of the field-free parameters is presented.Key words: calcium monohydride, molecular beam, fluorescence.
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38
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Krems RV, Dalgarno A. Quantum-mechanical theory of atom-molecule and molecular collisions in a magnetic field: Spin depolarization. J Chem Phys 2004; 120:2296-307. [PMID: 15268368 DOI: 10.1063/1.1636691] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A theory for quantum-mechanical calculations of cross sections for atom-molecule and molecular collisions in a magnetic field is presented. The formalism is based on the representation of the wave function as an expansion in a fully uncoupled space-fixed basis. The systems considered include 1S-atom-2Sigma-molecule, 1S-atom-3Sigma-molecule, 2Sigma-molecule-2Sigma-molecule, and 3Sigma-molecule-3Sigma-molecule. The theory is used to elucidate the mechanisms for collisionally induced spin depolarization.
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Affiliation(s)
- R V Krems
- Harvard-MIT Center for Ultracold Atoms, Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
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Balakrishnan N, Dalgarno A. On the Isotope Effect in F + HD Reaction at Ultracold Temperatures. J Phys Chem A 2003. [DOI: 10.1021/jp022654v] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- N. Balakrishnan
- Department of Chemistry, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, Nevada 89154
| | - A. Dalgarno
- Institute for Theoretical Atomic and Molecular Physics, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138
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