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Five-membered ring compounds from the ortho-benzyne + methyl radical reaction under interstellar conditions

Nature Astronomy (2023)Cite this article

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Abstract

Reactive open-shell species, such as radicals and biradicals, are key intermediates in the formation of (poly)cyclic hydrocarbon species in a variety of interstellar environments, ranging from cold molecular clouds to the outflows of carbon-rich stars. In this work, we identify the products of the o-benzyne + methyl radical reaction isomer-selectively by photoion mass-selected threshold photoelectron spectroscopy. We assign the benzyl (\({\mathrm{C}}_7{\mathrm{{H}}_7}^\cdot\)) radical as the sole intermediate of the association reaction. Subsequent hydrogen-atom loss from benzyl yields the five-membered ring species fulvenallene (FA), 1-ethynylcyclopentadiene (1ECP) and 2-ethynylcyclopentadiene (2ECP), which have recently been detected in the cold molecular cloud TMC-1. We report a comprehensive C7H7 potential energy surface of the title reaction and show that the products form via direct barrierless addition followed by ring contraction and hydrogen elimination. A statistical model predicts 89% 1ECP, 8% FA and 3% 2ECP branching ratios at 0 K. Astrochemical simulations of TMC-1 incorporating this reaction result in the excellent reproduction of the abundance of a five-membered ring species, 1ECP, and provide strong evidence for the in situ ‘bottom-up’ formation of small cyclic species in cold cores. Last, we put the results in context of the recent detection of fulvenallene in TMC-1.

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Fig. 1: The main species discussed in this work.
Fig. 2: Mass spectra at 9.5 eV photon energy and ~1,100 K pyrolysis temperature.
Fig. 3: Mass-selected threshold photoelectron spectra recorded at a temperature of 1,089 K.
Fig. 4: Summary of the C7H7 PES of the methyl + o-benzyne reaction.
Fig. 5: Formation rates for the various product channels of the methyl + o-benzyne reaction.
Fig. 6: Results from astrochemical simulations.

Data availability

The raw i2PEPICO datasets are available from the corresponding author upon reasonable request. Output files (.log files) from quantum chemical calculations are provided in Supplementary Data 1. Source data for the figures are provided with this paper.

Code availability

Quantum chemical calculations have been performed using Gaussian1663. Franck–Condon simulations have been performed using ezSpectrum33. Microcanonical rates have been calculated using the miniPEPICO programme64. Custom code used in this work as well as the chemical reaction network are available from C.N.S. (cshingledecker@benedictine.edu) upon request.

References

  1. Cernicharo, J. et al. Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey. Astron. Astrophys. 652, L9 (2021).

    Article  ADS  Google Scholar 

  2. Cernicharo, J. et al. Discovery of two isomers of ethynyl cyclopentadiene in TMC-1: abundances of CCH and CN derivatives of hydrocarbon cycles. Astron. Astrophys. 655, L1 (2021).

    Article  ADS  Google Scholar 

  3. McCarthy, M. C. et al. Interstellar detection of the highly polar five-membered ring cyanocyclopentadiene. Nat. Astron. 5, 176–180 (2021).

    Article  ADS  Google Scholar 

  4. McCarthy, M. C. & McGuire, B. A. Aromatics and cyclic molecules in molecular clouds: a new dimension of interstellar organic chemistry. J. Phys. Chem. A 125, 3231–3243 (2021).

    Article  Google Scholar 

  5. Cernicharo, J. et al. Pure hydrocarbon cycles in TMC-1: discovery of ethynyl cyclopropenylidene, cyclopentadiene, and indene. Astron. Astrophys. 649, L15 (2021).

    Article  ADS  Google Scholar 

  6. Burkhardt, A. M. et al. Discovery of the pure polycyclic aromatic hydrocarbon indene (c-C9H8) with GOTHAM observations of TMC-1. Astrophys. J. Lett. 913, L18 (2021).

    Article  ADS  Google Scholar 

  7. Lee, K. L. K. et al. Interstellar detection of 2-cyanocyclopentadiene, C5H5CN, a second five-membered ring toward TMC-1. Astrophys. J. Lett. 910, L2 (2021).

    Article  ADS  Google Scholar 

  8. McGuire, B. A. et al. Discovery of the interstellar polycyclic aromatic hydrocarbons 1- and 2-cyanonaphthalene. Science 371, 1265–1269 (2021).

    Article  ADS  Google Scholar 

  9. Herbst, E. & van Dishoeck, E. F. Complex organic interstellar molecules. Annu. Rev. Astron. Astrophys. 47, 427–480 (2009).

    Article  ADS  Google Scholar 

  10. Allamandola, L. J., Tielens, A. G. G. M. & Barker, J. R. Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands: auto exhaust along the milky way. Astrophys. J. Lett. 290, L25–L28 (1985).

    Article  ADS  Google Scholar 

  11. Leger, A. & Puget, J. L. Identification of the ‘unidentified’ IR emission features of interstellar dust? Astron. Astrophys. 137, L5–L8 (1984).

    ADS  Google Scholar 

  12. Tielens, A. Interstellar polycyclic aromatic hydrocarbon molecules. Annu. Rev. Astron. Astrophys. 46, 289–337 (2008).

    Article  ADS  Google Scholar 

  13. Frenklach, M. & Feigelson, E. D. Formation of polycyclic aromatic hydrocarbons in circumstellar envelopes. Astrophys. J. 341, 372–384 (1989).

    Article  ADS  Google Scholar 

  14. Cherchneff, I., Barker, J. R. & Tielens, A. G. G. M. Polycyclic aromatic hydrocarbon formation in carbon-rich stellar envelopes. Astrophys. J. 401, 269–287 (1992).

    Article  ADS  Google Scholar 

  15. Tielens, A. G. G. M. The molecular universe. Rev. Mod. Phys. 85, 1021–1081 (2013).

    Article  ADS  Google Scholar 

  16. McGuire, B. A. et al. Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering. Science 371, 1265–1269 (2021).

    Article  ADS  Google Scholar 

  17. Chabot, M., Béroff, K., Dartois, E., Pino, T. & Godard, M. Coulomb explosion of polycyclic aromatic hydrocarbons induced by heavy cosmic rays: carbon chains production rates. Astrophys. J. 888, 17 (2019).

    Article  ADS  Google Scholar 

  18. Burkhardt, A. M. et al. Ubiquitous aromatic carbon chemistry at the earliest stages of star formation. Nat. Astron. 5, 181–187 (2021).

    Article  ADS  Google Scholar 

  19. Abe, M. Diradicals. Chem. Rev. 113, 7011–7088 (2013).

    Article  Google Scholar 

  20. Brown, R. D., Godfrey, P. D. & Rodler, M. Microwave spectrum of benzyne. J. Am. Chem. Soc. 108, 1296–1297 (1986).

    Article  Google Scholar 

  21. Wenthold, P. G., Squires, R. R. & Lineberger, W. C. Ultraviolet photoelectron spectroscopy of the o-, m-, and p-benzyne negative ions. Electron affinities and singlet-triplet splittings for o-, m-, and p-benzyne. J. Am. Chem. Soc. 120, 5279–5290 (1998).

    Article  Google Scholar 

  22. Zhang, F., Parker, D., Kim, Y. S., Kaiser, R. I. & Mebel, A. M. On the formation of ortho-benzyne (o-C6H4) under single collision conditions and its role in interstellar chemistry. Astrophys. J. 728, 141 (2011).

    Article  ADS  Google Scholar 

  23. McCabe, M. N., Hemberger, P., Reusch, E., Bodi, A. & Bouwman, J. Off the beaten path: almost clean formation of indene from the ortho-benzyne + allyl reaction. J. Phys. Chem. Lett. 11, 2859–2863 (2020).

    Article  Google Scholar 

  24. Wakelam, V. et al. A Kinetic Database for Astrochemistry (KIDA). Astrophys. J. Suppl. Ser. 199, 21 (2012).

    Article  ADS  Google Scholar 

  25. Herzberg, G. The Bakerian lecture, the spectra and structures of free methyl and free methylene. Proc. R. Soc. Lond. 262, 291–317 (1961).

    ADS  Google Scholar 

  26. Yamada, C., Hirota, E. & Kawaguchi, K. Diode laser study of the ν2 band of the methyl radical. J. Chem. Phys. 75, 5256–5264 (1981).

    Article  ADS  Google Scholar 

  27. Feuchtgruber, H., Helmich, F. P., van Dishoeck, E. F. & Wright, C. M. Detection of interstellar CH3. Astrophys. J. 535, L111–L114 (2000).

    Article  ADS  Google Scholar 

  28. Kohn, D. W., Clauberg, H. & Chen, P. Flash pyrolysis nozzle for generation of radicals in a supersonic jet expansion. Rev. Sci. Instrum. 63, 4003–4005 (1992).

    Article  ADS  Google Scholar 

  29. Sztáray, B. et al. CRF-PEPICO: double velocity map imaging photoelectron photoion coincidence spectroscopy for reaction kinetics studies. J. Chem. Phys. 147, 013944 (2017).

    Article  ADS  Google Scholar 

  30. Bodi, A. et al. Imaging photoelectron photoion coincidence spectroscopy with velocity focusing electron optics. Rev. Sci. Instrum. 80, 034101 (2009).

    Article  ADS  Google Scholar 

  31. Bodi, A., Hemberger, P., Gerber, T. & Sztáray, B. A new double imaging velocity focusing coincidence experiment: i2PEPICO. Rev. Sci. Instrum. 83, 083105 (2012).

    Article  ADS  Google Scholar 

  32. Hemberger, P., van Bokhoven, J. A., Pérez-Ramírez, J. & Bodi, A. New analytical tools for advanced mechanistic studies in catalysis: photoionization and photoelectron photoion coincidence spectroscopy. Catal. Sci. Technol. 10, 1975–1990 (2021).

    Article  Google Scholar 

  33. Mozhayskiy, A. & Krylov, A. I. ezSpectrum v.3.0; http://iopenshell.usc.edu/downloads

  34. Montgomery, J. A., Frisch, M. J., Ochterski, J. W. & Petersson, G. A. A complete basis set model chemistry. VII. Use of the minimum population localization method. J. Chem. Phys. 112, 6532–6542 (2000).

    Article  ADS  Google Scholar 

  35. Ruaud, M., Wakelam, V. & Hersant, F. Gas and grain chemical composition in cold cores as predicted by the Nautilus three-phase model. Mon. Not. R. Astron. Soc. 459, 3756–3767 (2016).

    Article  ADS  Google Scholar 

  36. Bodi, A. et al. Controlling tunnelling in methane loss from acetone ions by deuteration. Phys. Chem. Chem. Phys. 17, 28505–28509 (2015).

    Article  Google Scholar 

  37. Bouwman, J., Bodi, A., Oomens, J. & Hemberger, P. On the formation of cyclopentadiene in the \({\mathrm{C}}_3{\mathrm{{H}}_5}^\cdot\) + C2H2 reaction. Phys. Chem. Chem. Phys. 17, 20508–20514 (2015).

    Article  Google Scholar 

  38. Zaleski, D. P. et al. Substitution reactions in the pyrolysis of acetone revealed through a modeling, experiment, theory paradigm. J. Am. Chem. Soc. 143, 3124–3142 (2021).

    Article  Google Scholar 

  39. Erman, P. et al. Direct determination of the ionization potential of CO by resonantly enhanced multiphoton ionization mass spectroscopy. Chem. Phys. Lett. 215, 173–178 (1993).

    Article  ADS  Google Scholar 

  40. Wei, L. et al. A vacuum ultraviolet photoionization mass spectrometric study of acetone. J. Phys. Chem. A 109, 4231–4241 (2005).

    Article  Google Scholar 

  41. Bieri, G., Burger, F., Heilbronner, E. & Maier, J. P. Valence ionization energies of hydrocarbons. Helv. Chim. Acta 60, 2213–2233 (1977).

    Article  Google Scholar 

  42. Blush, J. A. & Chen, P. Photoelectron spectrum of the vinyl radical: downward revision of the C2H3-ionization potential. J. Phys. Chem. 96, 4138–4140 (1992).

    Article  Google Scholar 

  43. Ruscic, B., Berkowitz, J., Curtiss, L. A. & Pople, J. A. The ethyl radical: photoionization and theoretical studies. J. Chem. Phys. 91, 114–121 (1989).

    Article  ADS  Google Scholar 

  44. Minsek, D. W. & Chen, P. Photoelectron spectrum of the propargyl radical in a supersonic beam. J. Phys. Chem. 94, 8399–8401 (1990).

    Article  Google Scholar 

  45. Dyke, J. M. Properties of gas-phase ions. Information to be obtained from photoelectron spectroscopy of unstable molecules. J. Chem. Soc. Faraday Trans. 2 83, 69–87 (1987).

    Article  Google Scholar 

  46. Kaiser, D. et al. The ortho-benzyne cation is not planar. Phys. Chem. Chem. Phys. 20, 3988–3996 (2018).

    Article  Google Scholar 

  47. Butcher, V., Costa, M. L., Dyke, J. M., Ellis, A. R. & Morris, A. A study of the phenyl radical by vacuum ultraviolet photoelectron spectroscopy. Chem. Phys. 115, 261–267 (1987).

    Article  Google Scholar 

  48. Nemeth, G. I., Selzle, H. L. & Schlag, E. W. Magnetic ZEKE experiments with mass analysis. Chem. Phys. Lett. 215, 151–155 (1993).

    Article  ADS  Google Scholar 

  49. Steinbauer, M., Hemberger, P., Fischer, I. & Bodi, A. Photoionization of C7H6 and C7H5: observation of the fulvenallenyl radical. Chemphyschem. 12, 1795–1797 (2011).

    Article  Google Scholar 

  50. Bouwman, J., Hrodmarsson, H. R., Ellison, G. B., Bodi, A. & Hemberger, P. Five birds with one stone: photoelectron photoion coincidence unveils rich phthalide pyrolysis chemistry. J. Phys. Chem. A 125, 1738–1746 (2021).

    Article  Google Scholar 

  51. NIST Chemistry WebBook SRD 69 (National Institute of Standards and Technology, 2009); http://webbook.nist.gov

  52. Fischer, K., Hemberger, P., Bodi, A. & Fischer, I. Photoionisation of the tropyl radical. Beilstein J. Org. Chem. 9, 681–688 (2013).

    Article  Google Scholar 

  53. Eiden, G. C., Weinhold, F. & Weisshaar, J. C. Photoelectron spectroscopy of free radicals with cm−1 resolution: the benzyl cation. J. Chem. Phys. 95, 8665–8668 (1991).

    Article  ADS  Google Scholar 

  54. Woon, D. E. & Herbst, E. Quantum chemical predictions of the properties of known and postulated neutral interstellar molecules. Astrophys. J. Suppl. Ser. 185, 273–288 (2009).

    Article  ADS  Google Scholar 

  55. Zhang, F. et al. A VUV photoionization study of the formation of the indene molecule and its isomers. J. Phys. Chem. Lett. 2, 1731–1735 (2011).

    Article  Google Scholar 

  56. Herbst, E. & Millar, T. J. Chapter 1 in Low Temperatures and Cold Molecules (ed. Smith, I. W. M.) (Imperial College Press, 2008).

  57. Shingledecker, C. N., Molpeceres, G., Rivilla, V. M., Majumdar, L. & Kästner, J. Isomers in interstellar environments. I. The case of Z- and E-cyanomethanimine. Astrophys. J. 897, 158 (2020).

    Article  ADS  Google Scholar 

  58. Loomis, R. A. et al. An investigation of spectral line stacking techniques and application to the detection of HC11N.Nat. Astron 5, 188–196 (2021).

    Article  ADS  Google Scholar 

  59. McCarthy, M. C. et al. Interstellar detection of the highly polar five-membered ring cyanocyclopentadiene. Nat. Astron. 5, 176–180 (2021).

    Article  ADS  Google Scholar 

  60. Cernicharo, J. et al. Discovery of fulvenallene in TMC-1 with the QUIJOTE line survey. Astron. Astrophys. 663, L9 (2022).

    Article  ADS  Google Scholar 

  61. South, M. S. & Liebeskind, L. S. Practical multigram syntheses of benzocyclobutenediones. J. Org. Chem. 47, 3815–3821 (1982).

    Article  Google Scholar 

  62. Sztáray, B. & Baer, T. Suppression of hot electrons in threshold photoelectron photoion coincidence spectroscopy using velocity focusing optics. Rev. Sci. Instrum. 74, 3763–3768 (2003).

    Article  ADS  Google Scholar 

  63. Frisch, M. J. et al. Gaussian 16 Revision A.03 (Gaussian Inc., 2016).

  64. Sztaray, B., Bodi, A. & Baer, T. Modeling unimolecular reactions in photoelectron photoion coincidence experiments. J. Mass Spectrom. 45, 1233–1245 (2010).

    Article  ADS  Google Scholar 

  65. Shingledecker, C. N. & Herbst, E. A general method for the inclusion of radiation chemistry in astrochemical models. Phys. Chem. Chem. Phys. 20, 5359–5367 (2018).

    Article  Google Scholar 

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Acknowledgements

J.B. acknowledges the Netherlands Organisation for Scientific Research (Nederlandse Organisatie voor Wetenschappelijk Onderzoek, NWO) for a Vidi grant (grant number 723.016.006). This work was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative (EINF-997). This work was supported in part by NASA’s Solar System Exploration Research Virtual Institute (SSERVI): Institute for Modeling Plasma, Atmosphere, and Cosmic Dust (IMPACT). The i2PEPICO experiments were performed at the VUV beamline at the SLS. P.H. and A.B. gratefully acknowledge funding by the Swiss Federal Office of Energy (BFE Contract Number SI/501269-01). We also wish to thank P. Ascher for technical assistance.

Author information

Authors and Affiliations

  1. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA

    Jordy Bouwman

  2. Department of Chemistry, University of Colorado, Boulder, CO, USA

    Jordy Bouwman

  3. Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT), NASA/SSERVI, Boulder, CO, USA

    Jordy Bouwman

  4. Laboratory for Astrophysics, Leiden Observatory, Leiden University, Leiden, the Netherlands

    Morgan N. McCabe

  5. Department of Physics and Astronomy, Benedictine College, Atchison, KS, USA

    Christopher N. Shingledecker, Joseph Wandishin & Virginia Jarvis

  6. Institute of Physical and Theoretical Chemistry, University of Würzburg, Würzburg, Germany

    Engelbert Reusch

  7. Laboratory for Synchrotron Radiation and Femtochemistry, Paul Scherrer Institute, Villigen, Switzerland

    Patrick Hemberger & Andras Bodi

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  1. Jordy Bouwman
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Contributions

J.B. wrote the manuscript with assistance from C.N.S., P.H. and A.B. The measurements were performed by J.B. and M.N.M with support from P.H. The experimental data were analysed by J.B. Potential energy surface calculations were performed by J.B. Ionization spectrum of the o-tolyl radical was simulated by P.H. The reaction entrance barrier of the reaction was characterized by A.B. The astrochemical reaction network was updated by J.W. and V.J. under supervision of C.N.S. Astrochemical simulations were performed by J.W. and V.J. under supervision of C.N.S. Rate coefficients were calculated by C.N.S., who also made the plots of the astrochemical simulation results. The ortho-benzyne precursor species, benzocyclobutenedione, was synthesised by E.R. The VUV beamline at the SLS where the measurements were conducted is managed by A.B.

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Correspondence to Jordy Bouwman.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–9, Tables 1 and 2 and supplementary discussion.

Supplementary Data 1

An archive file containing the Gaussian16 output (.log) files of the intermediates and transition states located on the potential energy surface.

Source data

Source Data Fig. 2

X–Y data of the mass spectra shown in Figure 2.

Source Data Fig. 3

X–Y data of the measured and simulated photoelectron spectra shown in Fig. 3.

Source Data Fig. 4

Energies of the intermediates and transition states located on the potential energy surface.

Source Data Fig. 5

Microcanonical rate data from our statistical model used to construct Fig. 5.

Source Data Fig. 6

Abundances of molecular species of interest as a function of time used to construct Fig. 6.

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Bouwman, J., McCabe, M.N., Shingledecker, C.N. et al. Five-membered ring compounds from the ortho-benzyne + methyl radical reaction under interstellar conditions. Nat Astron (2023). https://doi.org/10.1038/s41550-023-01893-2

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