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Photo-excitation of long-lived transient intermediates in ultracold reactions

Nature Physics volume 16, pages 1132–1136 (2020)Cite this article

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Abstract

In many chemical reactions, the transformation from reactants to products is mediated by transient intermediate complexes. For gas-phase reactions involving molecules with a few atoms, these complexes typically live on the order of 10 ps or less before dissociating, and are therefore rarely influenced by external processes. Here, we demonstrate that the transient intermediate complex K2Rb2*, formed from collisions between ultracold KRb molecules, undergoes rapid photo-excitation in the presence of a continuous-wave laser source at 1,064 nm, a wavelength commonly used to confine ultracold molecules. These excitations are facilitated by the exceptionally long lifetime of the complex under ultracold conditions. Indeed, by monitoring the change in the complex population after the sudden removal of the excitation light, we directly measure the lifetime of the complex to be 360 ± 30 ns, in agreement with our calculations based on the Rice–Ramsperger–Kassel–Marcus (RRKM) statistical theory. Our results shed light on the origin of the two-body loss widely observed in ultracold molecule experiments. Additionally, the long complex lifetime, coupled with the observed photo-excitation pathway, opens up the possibility to spectroscopically probe the structure of the complex with high resolution, thus elucidating the reaction dynamics.

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Fig. 1: Ultracold reactions in an optical dipole trap.
Fig. 2: Trap light-induced excitation of the intermediate complex.
Fig. 3: Energies and rates of the electronic excitations of the complex.
Fig. 4: Lifetime of the intermediate complex.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

Code availability

The computer codes used for theoretical calculations in this study are available from T.K. (tijs.karman@cfa.harvard.edu) upon reasonable request.

References

  1. Light, J. C. Statistical theory of bimolecular exchange reactions. Discuss. Faraday Soc. 44, 14–29 (1967).

    Article  Google Scholar 

  2. Herschbach, D. Reactive scattering. Faraday Discuss. Chem. Soc. 55, 233–251 (1973).

    Article  Google Scholar 

  3. Troe, J. The Polanyi Lecture. The colourful world of complex-forming bimolecular reactions. J. Chem. Soc. Faraday Trans. 90, 2303–2317 (1994).

    Article  Google Scholar 

  4. Su, Y.-T., Huang, Y.-H., Witek, H. A. & Lee, Y.-P. Infrared absorption spectrum of the simplest Criegee intermediate CH2OO. Science 340, 174–176 (2013).

    Article  ADS  Google Scholar 

  5. Bjork, B. J. et al. Direct frequency comb measurement of OD + CO → DOCO kinetics. Science 354, 444–448 (2016).

    Article  ADS  Google Scholar 

  6. Continetti, R. E. & Guo, H. Dynamics of transient species via anion photodetachment. Chem. Soc. Rev. 46, 7650–7667 (2017).

    Article  Google Scholar 

  7. Osborn, D. L. Reaction mechanisms on multiwell potential energy surfaces in combustion (and atmospheric) chemistry. Annu. Rev. Phys. Chem. 68, 233–260 (2017).

    Article  ADS  Google Scholar 

  8. Zewail, A. H. Femtochemistry: atomic-scale dynamics of the chemical bond. J. Phys. Chem. A 104, 5660–5694 (2000).

    Article  Google Scholar 

  9. Mayle, M., Quéméner, G., Ruzic, B. P. & Bohn, J. L. Scattering of ultracold molecules in the highly resonant regime. Phys. Rev. A 87, 012709 (2013).

    Article  ADS  Google Scholar 

  10. Hu, M.-G. et al. Direct observation of bimolecular reactions of ultracold KRb molecules. Science 366, 1111–1115 (2019).

    Article  ADS  Google Scholar 

  11. Quemener, G. & Julienne, P. S. Ultracold molecules under control! Chem. Rev. 112, 4949–5011 (2012).

    Article  Google Scholar 

  12. Balakrishnan, N. Perspective: ultracold molecules and the dawn of cold controlled chemistry. J. Chem. Phys. 145, 150901 (2016).

    Article  ADS  Google Scholar 

  13. Lique, F. et al. Cold Chemistry: Molecular Scattering and Reactivity Near Absolute Zero (Royal Society of Chemistry, 2017).

  14. Takekoshi, T. et al. Ultracold dense samples of dipolar RbCs molecules in the rovibrational and hyperfine ground state. Phys. Rev. Lett. 113, 205301 (2014).

    Article  ADS  Google Scholar 

  15. Ye, X., Guo, M., González-Martínez, M. L., Quéméner, G. & Wang, D. Collisions of ultracold 23Na87Rb molecules with controlled chemical reactivities. Sci. Adv. 4, eaaq0083 (2018).

    Article  ADS  Google Scholar 

  16. Gregory, P. D. et al. Sticky collisions of ultracold RbCs molecules. Nat. Commun. 10, 3104 (2019).

    Article  ADS  Google Scholar 

  17. Park, J. W., Will, S. A. & Zwierlein, M. W. Ultracold dipolar gas of fermionic 23Na40K molecules in their absolute ground state. Phys. Rev. Lett. 114, 205302 (2015).

    Article  ADS  Google Scholar 

  18. Santos, L., Shlyapnikov, G., Zoller, P. & Lewenstein, M. Bose–Einstein condensation in trapped dipolar gases. Phys. Rev. Lett. 85, 1791–1794 (2000).

    Article  ADS  Google Scholar 

  19. Büchler, H. P. et al. Strongly correlated 2D quantum phases with cold polar molecules: controlling the shape of the interaction potential. Phys. Rev. Lett. 98, 060404 (2007).

    Article  ADS  Google Scholar 

  20. Levinsen, J., Cooper, N. R. & Shlyapnikov, G. V. Topological px + ipy superfluid phase of fermionic polar molecules. Phys. Rev. A 84, 013603 (2011).

    Article  ADS  Google Scholar 

  21. Baranov, M. A., Dalmonte, M., Pupillo, G. & Zoller, P. Condensed matter theory of dipolar quantum gases. Chem. Rev. 112, 5012–5061 (2012).

    Article  Google Scholar 

  22. Christianen, A., Zwierlein, M. W., Groenenboom, G. C. & Karman, T. Photoinduced two-body loss of ultracold molecules. Phys. Rev. Lett. 123, 123402 (2019).

    Article  ADS  Google Scholar 

  23. Christianen, A., Karman, T. & Groenenboom, G. C. Quasiclassical method for calculating the density of states of ultracold collision complexes. Phys. Rev. A 100, 032708 (2019).

    Article  ADS  Google Scholar 

  24. Levine, R. D. Molecular Reaction Dynamics (Cambridge Univ. Press, 2009).

  25. Liu, Y., Grimes, D. D., Hu, M.-G. & Ni, K.-K. Probing ultracold chemistry using ion spectrometry. Phys. Chem. Chem. Phys. 22, 4861–4874 (2020).

    Article  Google Scholar 

  26. Vadla, C. et al. Comparison of theoretical and experimental red and near infrared absorption spectra in overheated potassium vapour. Eur. Phys. J. D 37, 37–49 (2006).

    Article  ADS  Google Scholar 

  27. Edvardsson, D., Lunell, S. & Marian, C. M. Calculation of potential energy curves for Rb2 including relativistic effects. Mol. Phys. 101, 2381–2389 (2003).

    Article  ADS  Google Scholar 

  28. Sato, H. Photodissociation of simple molecules in the gas phase. Chem. Rev. 101, 2687–2726 (2001).

    Article  Google Scholar 

  29. Noll, R. J., Yi, S. S. & Weisshaar, J. C. Bimolecular Ni+(2D5/2) + C3H8 reaction dynamics in real time. J. Phys. Chem. A 102, 386–394 (1998).

    Article  Google Scholar 

  30. Scherer, N., Sipes, C., Bernstein, R. & Zewail, A. Real-time clocking of bimolecular reactions: application to H + CO2. J. Chem. Phys. 92, 5239–5259 (1990).

    Article  ADS  Google Scholar 

  31. Ospelkaus, S. et al. Quantum-state controlled chemical reactions of ultracold potassium-rubidium molecules. Science 327, 853–857 (2010).

    Article  ADS  Google Scholar 

  32. Huber, K.-P. Molecular Spectra and Molecular Structure: IV. Constants of Diatomic Molecules (Springer, 2013).

  33. Amiot, C. Laser-induced fluorescence of Rb2: the (1)\({}^{1}{\Sigma }_{g}^{+}(X)\), (2)\({}^{1}{\Sigma }_{g}^{+}(X)\), (1)1Πu(B), (1)1Πg, and (2)1Πg(C) electronic states. J. Chem. Phys. 93, 8591–8604 (1990).

    Article  ADS  Google Scholar 

  34. Werner, H.-J. et al. Molpro, version 2019.2, a package of ab initio programs (Molpro, 2019); http://www.molpro.net

  35. De Marco, L. et al. A degenerate Fermi gas of polar molecules. Science 363, 853–856 (2019).

    Article  ADS  Google Scholar 

  36. Yao, N. Y., Zaletel, M. P., Stamper-Kurn, D. M. & Vishwanath, A. A quantum dipolar spin liquid. Nat. Phys. 14, 405–410 (2018).

    Article  Google Scholar 

  37. Gregory, P. D., Blackmore, J. A., Bromley, S. L. & Cornish, S. L. Loss of ultracold 87Rb 133Cs molecules via optical excitation of long-lived two-body collision complexes. Phys. Rev. Lett. 124, 163402 (2020).

    Article  ADS  Google Scholar 

  38. Fuentealba, P., Preuss, H., Stoll, H. & Von Szentpály, L. A proper account of core-polarization with pseudopotentials: single valence-electron alkali compounds. Chem. Phys. Lett. 89, 418–422 (1982).

    Article  ADS  Google Scholar 

  39. Christianen, A., Karman, T., Vargas-Hernández, R. A., Groenenboom, G. C. & Krems, R. V. Six-dimensional potential energy surface for NaK–NaK collisions: Gaussian process representation with correct asymptotic form. J. Chem. Phys. 150, 064106 (2019).

    Article  ADS  Google Scholar 

  40. Byrd, J. N., Montgomery, J. A. Jr & Côté, R. Structure and thermochemistry of K2Rb, KRb2, and K2Rb2. Phys. Rev. A 82, 010502 (2010).

    Article  ADS  Google Scholar 

  41. Yang, D. et al. A global full-dimensional potential energy surface for the K2Rb2 complex and its lifetime. J. Phys. Chem. Lett. 11, 2605–2610 (2020).

    Article  Google Scholar 

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Acknowledgements

We thank L. Zhu for experimental assistance. This work is supported by DOE YIP and the David and Lucile Packard Foundation. M.A.N. is supported by an HQI postdoctoral fellowship. T.K. is supported by NWO Rubicon grant no. 019.172EN.007 and the NSF through ITAMP. H.G. acknowledges a MURI grant from ARO (W911NF-19-1-0283) and a Humboldt Research Award.

Author information

Author notes

  1. These authors contributed equally: Yu Liu, Ming-Guang Hu.

Authors and Affiliations

  1. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA

    Yu Liu, Ming-Guang Hu, Matthew A. Nichols, David D. Grimes & Kang-Kuen Ni

  2. Department of Physics, Harvard University, Cambridge, MA, USA

    Yu Liu & Kang-Kuen Ni

  3. Harvard-MIT Center for Ultracold Atoms, Cambridge, MA, USA

    Yu Liu, Ming-Guang Hu, Matthew A. Nichols, David D. Grimes & Kang-Kuen Ni

  4. ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA

    Tijs Karman

  5. Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, NM, USA

    Hua Guo

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Contributions

The experimental work and data analysis were carried out by Y.L., M.-G.H., M.A.N., D.D.G. and K.-K.N. Theoretical calculations were performed by T.K., and H.G. aided in the analysis of the results. All authors contributed to interpreting the results and writing the manuscript.

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Correspondence to Kang-Kuen Ni.

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Extended data

Extended Data Fig. 1 Continued formation of products at high ODT intensities.

Steady-state K2+ (red circles) and Rb2+ (blue circles) ion counts at ODT light intensities in the 11.3–46.2 kW/cm2 range, normalized by the number of experimental cycles (~ 80 for each data point). The error bars represent shot noise. The dashed lines indicate the levels to which the ion counts plateau, obtained by averaging, within each dataset, the values of the points at ODT intensities larger than 15 kW/cm2. (Inset) Timing schemes of the ODT (red and blue) and the pulsed UV ionization laser (purple) used for the measurements presented here. The red (blue) trace corresponds to a high (low) duty cycle modulation of the ODT. The instantaneous ODT intensity, I, is inversely proportional to the duty cycle, while the time-averaged ODT intensity, Iavg is constant for all measurements.

Source Data

Source data

Source Data Fig. 1

K2+, Rb2+ (Fig. 2a) and K2Rb2+ (Fig. 2b) ion counts as a function of ODT intensity.

Source Data Fig. 4

Fig. 4a: oscilloscope traces of the 1,064-nm and UV ionization light intensities for the complex lifetime measurement. Fig. 4b: K2Rb2+ ion counts as a function of the delay between ODT turn-off edge and the UV ionization pulse.

Source Data Extended Data Fig. 1

K2+ and Rb2+ ion counts as a function of ODT intensity.

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Liu, Y., Hu, MG., Nichols, M.A. et al. Photo-excitation of long-lived transient intermediates in ultracold reactions. Nat. Phys. 16, 1132–1136 (2020). https://doi.org/10.1038/s41567-020-0968-8

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