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.
Subscribe to Journal
Get full journal access for 1 year
only $4.92 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Herbst, E. Chemistry of star-forming regions. J. Phys. Chem. A 109, 4017–4029 (2005).
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).
Sabbah, H. et al. Understanding reactivity at very low temperatures: the reactions of oxygen atoms with alkenes. Science 317, 102–105 (2007).
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).
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).
Bell, R. P. The Tunnel Effect in Chemistry 66 (Chapman & Hall, 1980).
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).
Xu, S. & Lin, M. C. Theoretical study on the kinetics for OH reactions with CH3OH and C2H5OH. Proc. Combust. Inst. 31, 159–166 (2007).
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).
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).
Herbst, E. Tunneling in the C2H–H2 reaction at low temperature. Chem. Phys. Lett. 222, 297–301 (1994).
Hess, W. P. & Tully, F. P. Hydrogen-atom abstraction from methanol by OH. J. Phys. Chem. 93, 1944–1947 (1989).
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).
Miller, W. H. Tunneling corrections to unimolecular rate constants, with application to formaldehyde. J. Am. Chem. Soc. 101, 6810–6814 (1979).
Garrett, B. C. & Truhlar, D. G. Semi-classical tunneling calculations. J. Phys. Chem. 83, 2921–2926 (1979).
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).
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).
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).
Weinreb, S., Barrett, A. H., Meeks, M. L. & Henry, J. C. Radio observations of OH in the interstellar medium. Nature 200, 829–831 (1963).
Harju, J., Winnberg, A. & Wouterloot, J. G. A. The distribution of OH in Taurus Molecular Cloud-1. Astron. Astrophys. 353, 1065–1073 (2000).
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).
Van Dishoeck, E. F. & Blake, G. A. Chemical evolution of star-forming regions. Annu. Rev. Astron. Astrophys. 36, 317–368 (1998).
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).
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).
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).
Shannon, R. J. Experimental and Computational Studies of Hydroxyl Radical Kinetics at Very Low Temperatures. PhD thesis, University of Leeds (2012).
Schreiner, P. R. et al. Methylhydroxycarbene: tunnelling control of a chemical reaction. Science 332, 1300–1303 (2011).
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).
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).
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).
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).
Miller, J. A. Combustion chemistry: elementary reactions to macroscopic processes. Faraday Discuss. 119, 461–475 (2001).
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.
The authors declare no competing financial interests.
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). https://doi.org/10.1038/nchem.1692
Photolysis of acetonitrile in a water-rich ice as a source of complex organic molecules: CH3CN and H2O:CH3CN ices
Astronomy & Astrophysics (2021)
Physics Reports (2021)
Science Advances (2021)
Nature Reviews Chemistry (2021)
Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices
Astronomy & Astrophysics (2021)