Enhanced reactivity of fluorine with para-hydrogen in cold interstellar clouds by resonance-induced quantum tunnelling


Chemical reactions are important in the evolution of low-temperature interstellar clouds, where the quantum tunnelling effect becomes significant. The F + para-H2 → HF + H reaction, which has a significant barrier of 1.8 kcal mol−1, is an important source of HF in interstellar clouds; however, the dynamics of this quantum-tunnelling-induced reactivity at low temperature is unknown. Here, we show that this quantum tunnelling is caused by a post-barrier resonance state. Quantum-state-resolved crossed-beam scattering measurements reveal that this resonance state has a collision energy of ~5 meV and a lifetime of ~80 fs, which are in excellent agreement with a recent anion photoelectron spectroscopic study. Accurate quantum reactive scattering calculations on the new iCSZ-LWAL potential energy surfaces provides a detailed explanation of the experimental results. The reaction rate for this system was also theoretically determined accurately at temperatures as low as 1 K.

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Fig. 1: TOF spectra of the H-atom product from the F + H2(v = 0, j = 0) → HF(v′) + H reaction at 180° in the centre-of-mass frame.
Fig. 2: QSSBSS of the F + H2(v = 0, j = 0) → HF(v′ = 2) + H reaction and photodetachment spectra of p-FH2.
Fig. 3: Three-dimensional product contour plots as a function of product velocity for the F + H2(v = 0, j = 0) → HF + H reaction.
Fig. 4: Schematic explaining the roles of the two resonances states (003) and (103) in the product channel in the reaction of F + H2(j = 0) and F + H2(j = 1).
Fig. 5: Calculated reaction rate constants.
Fig. 6: Calculated reaction rate constants.

Data availability

Data supporting the findings of this study are available from the corresponding authors on request.

Code availability

The accurate iCSZ and iCSZ-LWAL PESs developed in this work are available from the corresponding authors on request.


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C.X., Z.S., D.H.Z. and X.Y. acknowledge financial support for this research from the National Science Foundation of China (grants 21688102, 21590800, 21127902 and 21433009) and the Chinese Academy of Sciences (grants XDB 17010000). D.M.N. thanks the Air Force Office of Scientific Research for funding this research under grant no. FA9550-16-1-0097. M.H.A. thanks the US National Science Foundation for support under grant no. CHE-1565872.

Author information

X.Y., D.H.Z., Z.S., C.X., D.M.N. and M.H.A. conceived and supervised the research. The experiments were carried out by T.Y., L.H., T.W., D.D. and C.X. Data analysis and interpretation were performed by T.Y., L.H., T.W., D.D., C.X. and X.Y. Theoretical calculations were performed by Z.S., J.C., F.L., M.H.A. and D.H.Z. The manuscript was written by X.Y., Z.S., M.H.A., D.Z. and D.M.N., with contributions from all authors. All authors contributed to discussions about the content of the paper.

Correspondence to Millard H. Alexander or Zhigang Sun or Xueming Yang or Daniel M. Neumark.

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Supplementary Figs. 1–9, Supplementary Tables 1 and 2, Supplementary methods

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