Quantum phenomena in the translational motion of reactants, which are usually negligible at room temperature, can dominate reaction dynamics at low temperatures. In such cold conditions, even the weak centrifugal force is enough to create a potential barrier that keeps reactants separated. However, reactions may still proceed through tunnelling because, at low temperatures, wave-like properties become important. At certain de Broglie wavelengths, the colliding particles can become trapped in long-lived metastable scattering states, leading to sharp increases in the total reaction rate. Here, we show that these metastable states are responsible for a dramatic, order-of-magnitude-strong, quantum kinetic isotope effect by measuring the absolute Penning ionization reaction rates between hydrogen isotopologues and metastable helium down to 0.01 K. We demonstrate that measurements of a single isotope are insufficient to constrain ab initio calculations, making the kinetic isotope effect in the cold regime necessary to remove ambiguity among possible potential energy surfaces.
This is a preview of subscription content
Subscribe to Journal
Get full journal access for 1 year
only $9.92 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Urey, H., Brickwedde, F. & Murphy, G. A hydrogen isotope of mass 2. Phys. Rev. 39, 164–165 (1932).
Urey, H., Brickwedde, F. & Murphy, G. A hydrogen isotope of mass 2 and its concentration. Phys. Rev. 40, 1–15 (1932).
Washburn, E. W. & Urey, H. C. Concentration of the H2 isotope of hydrogen by the fractional electrolysis of water. Proc. Natl Acad. Sci. USA 18, 496–498 (1932).
Westheimer, F. H. The magnitude of the primary kinetic isotope effect for compounds of hydrogen and deuterium. Chem. Rev. 61, 265–273 (1961).
Ospelkaus, S. et al. Quantum-state controlled chemical reactions of ultracold potassium–rubidium molecules. Science 327, 853–857 (2010).
Henson, A. B., Gersten, S., Shagam, Y., Narevicius, J. & Narevicius, E. Observation of resonances in Penning ionization reactions at sub-kelvin temperatures in merged beams. Science 338, 234–238 (2012).
Ni, K-K. et al. Dipolar collisions of polar molecules in the quantum regime. Nature 464, 1324–1328 (2010).
Chefdeville, S. et al. Observation of partial wave resonances in low-energy O2–H2 inelastic collisions. Science 341, 1094–1096 (2013).
Millar, T. J. Deuterium fractionation in interstellar clouds. Space Sci. Rev. 106, 73–86 (2003).
Millar, T. J., Bennett, A. & Herbst, E. Deuterium fractionation in dense interstellar clouds. Astrophys. J. 340, 906 (1989).
Messenger, S. Identification of molecular-cloud material in interplanetary dust particles. Nature 404, 968–971 (2000).
Bell, M. T., Bell, P. & Softley, T. Ultracold molecules and ultracold chemistry. Mol. Phys. 107, 99–132 (2009).
Wigner, E. On the behavior of cross sections near thresholds. Phys. Rev. 73, 1002–1009 (1948).
Krems, R. V. Molecules near absolute zero and external field control of atomic and molecular dynamics. Int. Rev. Phys. Chem. 24, 99–118 (2005).
Herschbach, D. Molecular collisions, from warm to ultracold. Faraday Discuss. 142, 9 (2009).
Skodje, R. T. et al. Observation of a transition state resonance in the integral cross section of the F + HD reaction. J. Chem. Phys. 112, 4536 (2000).
Skodje, R. et al. Resonance-mediated chemical reaction: F + HD→HF + D. Phys. Rev. Lett. 85, 1206–1209 (2000).
Qiu, M. et al. Observation of Feshbach resonances in the F + H2→HF + H reaction. Science 311, 1440–1443 (2006).
Ren, Z. et al. Probing the resonance potential in the F atom reaction with hydrogen deuteride with spectroscopic accuracy. Proc. Natl Acad. Sci. USA 105, 12662–12666 (2008).
Kirste, M. et al. Quantum-state resolved bimolecular collisions of velocity-controlled OH with NO radicals. Science 338, 1060–1063 (2012).
Janssen, L. M. C., van der Avoird, A. & Groenenboom, G. C. Quantum reactive scattering of ultracold NH(X3Σ−) radicals in a magnetic trap. Phys. Rev. Lett. 110, 063201 (2013).
Janssen, L. M. C., Żuchowski, P. S., van der Avoird, A., Hutson, J. M. & Groenenboom, G. C. Cold and ultracold NH–NH collisions: the field-free case. J. Chem. Phys. 134, 124309 (2011).
Druyvesteyn, M. & Penning, F. The mechanism of electrical discharges in gases of low pressure. Rev. Mod. Phys. 12, 87–174 (1940).
Wiley, W. C. & McLaren, I. H. Time-of-flight mass spectrometer with improved resolution. Rev. Sci. Instrum. 26, 1150 (1955).
Siska, P. E. Molecular-beam studies of Penning ionization. Rev. Mod. Phys. 65, 337–412 (1993).
Hapka, M., Chałasiński, G., Kłos, J. & Żuchowski, P. S. First-principle interaction potentials for metastable He(3S) and Ne(3P) with closed-shell molecules: application to Penning-ionizing systems. J. Chem. Phys. 139, 014307 (2013).
Żuchowski, P. & Hutson, J. Low-energy collisions of NH3 and ND3 with ultracold Rb atoms. Phys. Rev. A 79, 062708 (2009).
Janssen, L. M. C., Żuchowski, P. S., van der Avoird, A., Groenenboom, G. C. & Hutson, J. M. Cold and ultracold NH–NH collisions in magnetic fields. Phys. Rev. A 83, 022713 (2011).
Even, U., Jortner, J., Noy, D., Lavie, N. & Cossart-Magos, C. Cooling of large molecules below 1 K and He clusters formation. J. Chem. Phys. 112, 8068 (2000).
Luria, K., Lavie, N. & Even, U. Dielectric barrier discharge source for supersonic beams. Rev. Sci. Instrum. 80, 104102 (2009).
Shagam, Y. & Narevicius, E. Sub-kelvin collision temperatures in merged neutral beams by correlation in phase-space. J. Phys. Chem. C 117, 22454–22461 (2013).
Chefdeville, S. et al. Appearance of low energy resonances in CO–para-H2 inelastic collisions. Phys. Rev. Lett. 109, 1–5 (2012).
The authors thank U. Even and Y. Prior for discussions. The authors thank J.W. Rosenberg for reading the manuscript. This research was made possible, in part, by the historic generosity of the Harold Perlman family. E.N. acknowledges support from the Israel Science Foundation and the Minerva Foundation. J.K. acknowledges financial support through the United States National Science Foundation (grant no. CHE-1213332) to M. Alexander. P.S.Z. was supported by the Iuventus Plus grant by the Polish Ministry of Science and Higher Education.
The authors declare no competing financial interests.
About this article
Cite this article
Lavert-Ofir, E., Shagam, Y., Henson, A. et al. Observation of the isotope effect in sub-kelvin reactions. Nature Chem 6, 332–335 (2014). https://doi.org/10.1038/nchem.1857
Nature Chemistry (2022)
Nature Chemistry (2022)
Determining the nature of quantum resonances by probing elastic and reactive scattering in cold collisions
Nature Chemistry (2021)
Nature Reviews Chemistry (2021)
Selectivity of weak intermolecular forces and precursor state of elementary oxidation reactions, a new insight on Ne* + N2 chemiionization
Scientific Reports (2021)