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Explanation of efficient quenching of molecular ion vibrational motion by ultracold atoms.

Stoecklin T, Halvick P, Gannouni MA, Hochlaf M, Kotochigova S, Hudson ER - Nat Commun (2016)

Bottom Line: Here, we theoretically explain the recently observed exception to this rule: efficient vibrational cooling of BaCl(+) by a laser-cooled Ca buffer gas.We perform intense close-coupling calculations that agree with the experimental result, and use both quantum defect theory and a statistical capture model to provide an intuitive understanding of the system.This result establishes that, in contrast to the commonly held opinion, there exists a large class of systems that exhibit efficient vibrational cooling and therefore supports a new route to realize the long-sought opportunities offered by molecular structure.

View Article: PubMed Central - PubMed

Affiliation: Université de Bordeaux, Institut des Sciences Moléculaires, UMR 5255 CNRS, 33405 Talence, France.

ABSTRACT
Buffer gas cooling of molecules to cold and ultracold temperatures is a promising technique for realizing a host of scientific and technological opportunities. Unfortunately, experiments using cryogenic buffer gases have found that although the molecular motion and rotation are quickly cooled, the molecular vibration relaxes at impractically long timescales. Here, we theoretically explain the recently observed exception to this rule: efficient vibrational cooling of BaCl(+) by a laser-cooled Ca buffer gas. We perform intense close-coupling calculations that agree with the experimental result, and use both quantum defect theory and a statistical capture model to provide an intuitive understanding of the system. This result establishes that, in contrast to the commonly held opinion, there exists a large class of systems that exhibit efficient vibrational cooling and therefore supports a new route to realize the long-sought opportunities offered by molecular structure.

No MeSH data available.


Related in: MedlinePlus

Comparison of quenching rates for present and previously studied systems.Close coupling vibrational quenching rate coefficients k10CC(T) for five different colliding systems with the diatomic cation in the initial state (ν=1,j=0).
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f7: Comparison of quenching rates for present and previously studied systems.Close coupling vibrational quenching rate coefficients k10CC(T) for five different colliding systems with the diatomic cation in the initial state (ν=1,j=0).

Mentions: This relation can be formally introduced through a capture statistical approach, which was presented in the body of this manuscript. This simple relation makes the vibrational quenching proportional not only to the De/ωe ratio but also to the polarizability of the ultra cold atom and to the relative mass of the system. These two last results were expected as they express the dependence of the quenching efficiency on the strength of the long-range interaction potential and on the density of states of the complex. The increase of the state density increases the lifetime of the complex and facilitates vibrational quenching. We notice, however, that the 4He-CH+ system seems to behave differently than the other systems. This is effectively what can be seen on Fig. 7 where the Close coupling rate coefficients were reported for these five systems in the [10−7, 1] Kelvin interval. The 4He-CH+ rate coefficient is the only one for which the rate coefficient decreases instead of increasing above the Wigner regime. This behaviour was shown in our paper dedicated to this system12 to be due to virtual state scattering38. This is indeed the only one of these five systems for which the real part of the scattering length is negative. Virtual state scattering increases the close coupling value of the quenching rate coefficient and our simple model then allows predicting a lower bound for the zero temperature limit for all the studied systems.


Explanation of efficient quenching of molecular ion vibrational motion by ultracold atoms.

Stoecklin T, Halvick P, Gannouni MA, Hochlaf M, Kotochigova S, Hudson ER - Nat Commun (2016)

Comparison of quenching rates for present and previously studied systems.Close coupling vibrational quenching rate coefficients k10CC(T) for five different colliding systems with the diatomic cation in the initial state (ν=1,j=0).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837476&req=5

f7: Comparison of quenching rates for present and previously studied systems.Close coupling vibrational quenching rate coefficients k10CC(T) for five different colliding systems with the diatomic cation in the initial state (ν=1,j=0).
Mentions: This relation can be formally introduced through a capture statistical approach, which was presented in the body of this manuscript. This simple relation makes the vibrational quenching proportional not only to the De/ωe ratio but also to the polarizability of the ultra cold atom and to the relative mass of the system. These two last results were expected as they express the dependence of the quenching efficiency on the strength of the long-range interaction potential and on the density of states of the complex. The increase of the state density increases the lifetime of the complex and facilitates vibrational quenching. We notice, however, that the 4He-CH+ system seems to behave differently than the other systems. This is effectively what can be seen on Fig. 7 where the Close coupling rate coefficients were reported for these five systems in the [10−7, 1] Kelvin interval. The 4He-CH+ rate coefficient is the only one for which the rate coefficient decreases instead of increasing above the Wigner regime. This behaviour was shown in our paper dedicated to this system12 to be due to virtual state scattering38. This is indeed the only one of these five systems for which the real part of the scattering length is negative. Virtual state scattering increases the close coupling value of the quenching rate coefficient and our simple model then allows predicting a lower bound for the zero temperature limit for all the studied systems.

Bottom Line: Here, we theoretically explain the recently observed exception to this rule: efficient vibrational cooling of BaCl(+) by a laser-cooled Ca buffer gas.We perform intense close-coupling calculations that agree with the experimental result, and use both quantum defect theory and a statistical capture model to provide an intuitive understanding of the system.This result establishes that, in contrast to the commonly held opinion, there exists a large class of systems that exhibit efficient vibrational cooling and therefore supports a new route to realize the long-sought opportunities offered by molecular structure.

View Article: PubMed Central - PubMed

Affiliation: Université de Bordeaux, Institut des Sciences Moléculaires, UMR 5255 CNRS, 33405 Talence, France.

ABSTRACT
Buffer gas cooling of molecules to cold and ultracold temperatures is a promising technique for realizing a host of scientific and technological opportunities. Unfortunately, experiments using cryogenic buffer gases have found that although the molecular motion and rotation are quickly cooled, the molecular vibration relaxes at impractically long timescales. Here, we theoretically explain the recently observed exception to this rule: efficient vibrational cooling of BaCl(+) by a laser-cooled Ca buffer gas. We perform intense close-coupling calculations that agree with the experimental result, and use both quantum defect theory and a statistical capture model to provide an intuitive understanding of the system. This result establishes that, in contrast to the commonly held opinion, there exists a large class of systems that exhibit efficient vibrational cooling and therefore supports a new route to realize the long-sought opportunities offered by molecular structure.

No MeSH data available.


Related in: MedlinePlus