Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling


Understanding the abundances of molecules in dense interstellar clouds requires knowledge of the rates of gas-phase reactions between uncharged species. However, because of the low temperatures within these clouds, reactions with an activation barrier were considered too slow to play an important role. Here we show that, despite the presence of a barrier, the rate coefficient for the reaction between the hydroxyl radical (OH) and methanol—one of the most abundant organic molecules in space—is almost two orders of magnitude larger at 63 K than previously measured at 200 K. We also observe the formation of the methoxy radical product, which was recently detected in space. These results are interpreted by the formation of a hydrogen-bonded complex that is sufficiently long-lived to undergo quantum-mechanical tunnelling to form products. We postulate that this tunnelling mechanism for the oxidation of organic molecules by OH is widespread in low-temperature interstellar environments.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Schematic potential energy surface for the reaction between OH and methanol based on the calculations of Xu and Lin8 with all energies given in kJ mol−1 relative to the reagents.
Figure 2: Temperature dependence of the rate coefficient k1 for the reaction of OH radicals with methanol, plotted in Arrhenius form together with a theoretical calculation.
Figure 3: Removal of hydroxyl (OH) radicals and production of methoxy (CH3O) radicals in the reaction of OH with methanol at 82 K.
Figure 4: Variation of the rate coefficient for the reaction of OH with methanol as a function of total gas density at 82 ± 4 K.
Figure 5: Rate coefficients for the dissociation back to reactants (black) and the product-forming channel (red) as a function of energy within the initially formed OH–methanol complex.


  1. 1

    Herbst, E. Chemistry of star-forming regions. J. Phys. Chem. A 109, 4017–4029 (2005).

    CAS  Article  Google Scholar 

  2. 2

    Smith, I. W. M., Herbst, E. & Chang, Q. Rapid neutral–neutral reactions at low temperatures: a new network and first results for TMC-1. Mon. Not. R. Astron. Soc. 350, 323–330 (2004).

    CAS  Article  Google Scholar 

  3. 3

    Sabbah, H. et al. Understanding reactivity at very low temperatures: the reactions of oxygen atoms with alkenes. Science 317, 102–105 (2007).

    CAS  Article  Google Scholar 

  4. 4

    Smith, I. W. M., Sage, A. M., Donahue, N. M., Herbst, E. & Quan, D. The temperature-dependence of rapid low temperature reactions: experiment, understanding and prediction. Faraday Discuss. 133, 137–156 (2006).

    CAS  Article  Google Scholar 

  5. 5

    Dillon, T. J., Holscher, D., Sivakumaran, V., Horowitz, A. & Crowley, J. N. A. Kinetics of the reactions of HO with methanol (210–351 K) and with ethanol (216–368 K). Phys. Chem. Chem. Phys. 7, 349–355 (2005).

    CAS  Article  Google Scholar 

  6. 6

    Bell, R. P. The Tunnel Effect in Chemistry 66 (Chapman & Hall, 1980).

    Google Scholar 

  7. 7

    Smith, I. W. M. & Ravishankara, A. R. Role of hydrogen-bonded intermediates in the bimolecular reactions of the hydroxyl radical. J. Phys. Chem. A 106, 4798–4807 (2002).

    CAS  Article  Google Scholar 

  8. 8

    Xu, S. & Lin, M. C. Theoretical study on the kinetics for OH reactions with CH3OH and C2H5OH. Proc. Combust. Inst. 31, 159–166 (2007).

    Article  Google Scholar 

  9. 9

    Brown, S. S., Burkholder, J. B., Talukdar, R. K. & Ravishankara, A. R. Reaction of hydroxyl radical with nitric acid: insights into its mechanism. J. Phys. Chem. A 105, 1605–1614 (2001).

    CAS  Article  Google Scholar 

  10. 10

    Xia, W. S. & Lin, M. C. A multifacet mechanism for the OH + HNO3 reaction: an ab initio molecular orbital/statistical theory study. J. Chem. Phys. 114, 4522–4532 (2001).

    CAS  Article  Google Scholar 

  11. 11

    Herbst, E. Tunneling in the C2H–H2 reaction at low temperature. Chem. Phys. Lett. 222, 297–301 (1994).

    CAS  Article  Google Scholar 

  12. 12

    Hess, W. P. & Tully, F. P. Hydrogen-atom abstraction from methanol by OH. J. Phys. Chem. 93, 1944–1947 (1989).

    CAS  Article  Google Scholar 

  13. 13

    Wallington, T. J. & Kurylo, M. J. The gas-phase reactions of hydroxyl radicals with a series of aliphatic-alcohols over the temperature-range 240–440-K. Int. J. Chem. Kinet. 19, 1015–1023 (1987).

    CAS  Article  Google Scholar 

  14. 14

    Miller, W. H. Tunneling corrections to unimolecular rate constants, with application to formaldehyde. J. Am. Chem. Soc. 101, 6810–6814 (1979).

    CAS  Article  Google Scholar 

  15. 15

    Garrett, B. C. & Truhlar, D. G. Semi-classical tunneling calculations. J. Phys. Chem. 83, 2921–2926 (1979).

    CAS  Article  Google Scholar 

  16. 16

    Pu, J. Z. & Truhlar, D. G. Validation of variational transition state theory with multidimensional tunneling contributions against accurate quantum mechanical dynamics for H + CH4 → H2 + CH3 in an extended temperature interval. J. Chem. Phys. 117, 1479–1481 (2002).

    CAS  Article  Google Scholar 

  17. 17

    Carpenter, B. K. Heavy-atom tunneling as the dominant pathway in a solution-phase reaction? Bond shift in antiaromatic annulenes. J. Am. Chem. Soc. 105, 1700–1701 (1983).

    CAS  Article  Google Scholar 

  18. 18

    McCaulley, J. A., Kelly, N., Golde, M. F. & Kaufman, F. Kinetic-studies of the reactions of F and OH with CH3OH. J. Phys. Chem. 93, 1014–1018 (1989).

    CAS  Article  Google Scholar 

  19. 19

    Weinreb, S., Barrett, A. H., Meeks, M. L. & Henry, J. C. Radio observations of OH in the interstellar medium. Nature 200, 829–831 (1963).

    CAS  Article  Google Scholar 

  20. 20

    Harju, J., Winnberg, A. & Wouterloot, J. G. A. The distribution of OH in Taurus Molecular Cloud-1. Astron. Astrophys. 353, 1065–1073 (2000).

    CAS  Google Scholar 

  21. 21

    Herbst, E. in Atoms, Ions and Molecules: New Results in Spectral Line Astrophysics, ASP Conference Series Vol. 16 (eds Haschick, A. D. & Ho, P. T. P.) 313–322 (Publ. Astron. Soc. Pacif. 1991).

    Google Scholar 

  22. 22

    Van Dishoeck, E. F. & Blake, G. A. Chemical evolution of star-forming regions. Annu. Rev. Astron. Astrophys. 36, 317–368 (1998).

    Article  Google Scholar 

  23. 23

    Cernicharo, J. et al. Discovery of the methoxy radical, CH3O, towards B1: Dust grain and gas-phase chemistry in cold dark clouds. Astrophys. J. Lett. 759, L43 (2012).

    Article  Google Scholar 

  24. 24

    Cheung, A. C., Rank, D. M., Townes, C. H., Thornton, D. D. & Welch, W. J. Detection of NH3 molecules in the interstellar medium by their microwave emission. Phys. Rev. Lett. 21, 1701–1705 (1983).

    Article  Google Scholar 

  25. 25

    Diau, E. W. G., Tso, T. L. & Lee, Y. P. Kinetics of the reaction OH + NH3 in the range 273–433 K. J. Phys. Chem. 94, 5261–5265 (1990).

    CAS  Article  Google Scholar 

  26. 26

    Shannon, R. J. Experimental and Computational Studies of Hydroxyl Radical Kinetics at Very Low Temperatures. PhD thesis, University of Leeds (2012).

    Google Scholar 

  27. 27

    Schreiner, P. R. et al. Methylhydroxycarbene: tunnelling control of a chemical reaction. Science 332, 1300–1303 (2011).

    CAS  Article  Google Scholar 

  28. 28

    Shannon, R. J., Taylor, S., Goddard, A., Blitz, M. A. & Heard, D. E. Observation of a large negative temperature dependence for rate coefficients of reactions of OH with oxygenated volatile organic compounds studied at 86–112 K. Phys. Chem. Chem. Phys. 12, 13511–13514 (2010).

    CAS  Article  Google Scholar 

  29. 29

    Taylor, S. E., Goddard, A., Blitz, M. A., Cleary, P. A. & Heard, D. E. Pulsed Laval nozzle study of the kinetics of OH with unsaturated hydrocarbons at very low temperatures. Phys. Chem. Chem. Phys. 10, 422–437 (2008).

    CAS  Article  Google Scholar 

  30. 30

    Glowacki, D. R., Liang, C. H., Morley, C., Pilling, M. J. & Robertson, S. H. MESMER: an open-source master equation solver for multi-energy well reactions. J. Phys. Chem. A 116, 9545–9560 (2012).

    CAS  Article  Google Scholar 

  31. 31

    Seakins, P. W. et al. Kinetics of the unimolecular decomposition of iso-C3H7—weak collision effects in helium, argon, and nitrogen. J. Phys. Chem. 97, 4450–4458 (1993).

    CAS  Article  Google Scholar 

  32. 32

    Miller, J. A. Combustion chemistry: elementary reactions to macroscopic processes. Faraday Discuss. 119, 461–475 (2001).

    CAS  Article  Google Scholar 

Download references


This work received funding from the Natural Environment Research Council through the provision of a PhD studentship (R.J.S.) and for A.G. The National Centre for Atmospheric Science provides funding for M.A.B. and D.E.H. The authors thank the mechanical and electronics workshops within the School of Chemistry, the University of Leeds, for technical assistance.

Author information




R.J.S., M.A.B., A.G. and D.E.H. conceived and designed the experiments and analysed the data. R.J.S. and M.A.B. performed the experiments. R.J.S., M.A.B. and D.E.H. co-wrote the paper.

Corresponding author

Correspondence to Dwayne E. Heard.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary information

Supplementary information (PDF 1979 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Shannon, R., Blitz, M., Goddard, A. et al. Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling. Nature Chem 5, 745–749 (2013).

Download citation

Further reading


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing