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The effect of solvation on electron capture revealed using anion two-dimensional photoelectron spectroscopy


The reaction of low-energy electrons with neutral molecules to form anions plays an important role in chemistry, being involved in, for example, various biological and astrochemical processes. However, key aspects of electron–molecule interactions, such as the effect of incremental solvation on the initially excited electronic resonances, remain poorly understood. Here two-dimensional photoelectron spectroscopy of anionic anthracene and nitrogen-substituted derivatives—solvated by up to five water molecules—reveals that for an incoming electron, resonances red-shift with increasing hydration; but for the anion, the excitation energies of the resonances remain essentially the same. These complementary points of view show that the observed onset of enhanced anion formation for a specific cluster size is mediated by a bound excited state of the anion. Our findings suggest that polycyclic aromatic hydrocarbons may be more efficient at electron capture than previously predicted with important consequences for the ionization fraction in dense molecular clouds.

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Fig. 1: 2D photoelectron spectra of PA(N)H water cluster anions.
Fig. 2: Energies of electronic states of PA(N)H water cluster anions.
Fig. 3: Photoelectron spectra of C14H10 and C14H10(H2O)3.
Fig. 4: Schematic of the electron capture process by a PAH in the presence of water molecules.

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Data availability

The raw photoelectron images that are used to construct Fig. 1, together with their photoelectron spectra, are available at All other results are derived from these data. Source data are provided with this paper.

Code availability

Photoelectron images have been analysed using polar onion peeling, which is available at (Matlab version) or (Labview version).


  1. Alizadeh, E. & Sanche, L. Precursors of solvated electrons in radiobiological physics and chemistry. Chem. Rev. 112, 5578–5602 (2012).

    Article  CAS  PubMed  Google Scholar 

  2. Boudaı̈ffa, B., Cloutier, P., Hunting, D., Huels, M. A. & Sanche, L. Resonant formation of DNA strand breaks by low-energy (3 to 20 eV) electrons. Science 287, 1658–1660 (2000).

    Article  PubMed  Google Scholar 

  3. Ingólfsson, O. Low-energy Electrons: Fundamentals and Applications (CRC Press, 2019).

  4. Fabrikant, I. I., Caprasecca, S., Gallup, G. A. & Gorfinkiel, J. D. Electron attachment to molecules in a cluster environment. J. Chem. Phys. 136, 184301 (2012).

    Article  CAS  PubMed  Google Scholar 

  5. Smyth, M., Kohanoff, J. & Fabrikant, I. I. Electron-induced hydrogen loss in uracil in a water cluster environment. J. Chem. Phys. 140, 184313 (2014).

    Article  CAS  PubMed  Google Scholar 

  6. Kočišek, J., Pysanenko, A., Fárník, M. & Fedor, J. Microhydration prevents fragmentation of uracil and thymine by low-energy electrons. J. Phys. Chem. Lett. 7, 3401–3405 (2016).

    Article  PubMed  Google Scholar 

  7. Sieradzka, A. & Gorfinkiel, J. D. Theoretical study of resonance formation in microhydrated molecules. I. Pyridine–(H2O)n, n = 1,2,3,5. J. Chem. Phys. 147, 034302 (2017).

    Article  PubMed  Google Scholar 

  8. McAllister, M. et al. Solvation effects on dissociative electron attachment to thymine. J. Phys. Chem. B 123, 1537–1544 (2019).

    Article  CAS  PubMed  Google Scholar 

  9. Lengyel, J. et al. Electron-triggered chemistry in HNO3/H2O complexes. Phys. Chem. Chem. Phys. 19, 11753–11758 (2017).

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  10. Poštulka, J., Slavíček, P., Fedor, J., Fárník, M. & Kočišek, J. Energy transfer in microhydrated uracil, 5-fluorouracil, and 5-bromouracil. J. Phys. Chem. B 121, 8965–8974 (2017).

    Article  PubMed  Google Scholar 

  11. Meißner, R. et al. Low-energy electrons transform the nimorazole molecule into a radiosensitiser. Nat. Commun. 10, 2388 (2019).

    Article  PubMed  PubMed Central  Google Scholar 

  12. Schulz, G. J. Resonances in electron impact on diatomic molecules. Rev. Mod. Phys. 45, 423–486 (1973).

    Article  CAS  Google Scholar 

  13. Christophorou, L. G. Electron–Molecule Interactions and their Applications (Academic Press, 1984).

  14. Horke, D. A., Li, Q., Blancafort, L. & Verlet, J. R. R. Ultrafast above-threshold dynamics of the radical anion of a prototypical quinone electron-acceptor. Nat. Chem. 5, 711–717 (2013).

    Article  CAS  PubMed  Google Scholar 

  15. Jordan, K. D. & Burrow, P. D. Temporary anion states of polyatomic hydrocarbons. Chem. Rev. 87, 557–588 (1987).

    Article  CAS  Google Scholar 

  16. Regeta, K. & Allan, M. Autodetachment dynamics of acrylonitrile anion revealed by two-dimensional electron impact spectra. Phys. Rev. Lett. 110, 203201 (2013).

    Article  CAS  PubMed  Google Scholar 

  17. Anstöter, C. S., Bull, J. N. & Verlet, J. R. R. Ultrafast dynamics of temporary anions probed through the prism of photodetachment. Int. Rev. Phys. Chem. 35, 509–538 (2016).

    Article  Google Scholar 

  18. Anstöter, C. S. et al. Mode-specific vibrational autodetachment following excitation of electronic resonances by electrons and photons. Phys. Rev. Lett. 124, 203401 (2020).

    Article  PubMed  Google Scholar 

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

    Article  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  21. Omont, A. Physics and chemistry of interstellar polycyclic aromatic molecules. Astron. Astrophys. 164, 159–178 (1986).

    CAS  Google Scholar 

  22. Lepp, S. & Dalgarno, A. Polycyclic aromatic hydrocarbons in interstellar chemistry. Astrophys. J. 324, 553–556 (1988).

    Article  CAS  Google Scholar 

  23. Allamandola, L. J., Tielens, A. G. G. M. & Barker, J. R. Interstellar polycyclic aromatic hydrocarbons—the infrared emission bands, the excitation/emission mechanism, and the astrophysical implications. Astrophys. J. Suppl. Ser. 71, 733–775 (1989).

    Article  CAS  PubMed  Google Scholar 

  24. Wakelam, V. & Herbst, E. Polycyclic aromatic hydrocarbons in dense cloud chemistry. Astrophys. J. 680, 371–383 (2008).

    Article  CAS  Google Scholar 

  25. Draine, B. T. Physics of the Interstellar and Intergalactic Medium (Princeton University Press, 2011).

  26. Allamandola, L. J., Bernstein, M. P., Sandford, S. A. & Walker, R. L. Evolution of interstellar ices. Space Sci. Rev. 90, 219–232 (1999).

    Article  CAS  PubMed  Google Scholar 

  27. Geers, V. C. et al. Lack of PAH emission toward low-mass embedded young stellar objects. Astron. Astrophys. 495, 837–846 (2009).

    Article  CAS  Google Scholar 

  28. Bergin, E. A. & Tafalla, M. Cold dark clouds: the initial conditions for star formation. Annu. Rev. Astron. Astrophys. 45, 339–396 (2007).

    Article  CAS  Google Scholar 

  29. Boogert, A. C. A. et al. The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects. I. H2O and the 5–8 μm bands. Astrophys. J. 678, 985–1004 (2008).

  30. Garcia-Sanz, A., Carelli, F., Sebastianelli, F., Gianturco, F. A. & Garcia, G. Dynamics of formation of anthracene anions in molecular clouds and protoplanetary atmospheres. New J. Phys. 15, 013018 (2013).

    Article  CAS  Google Scholar 

  31. Mensa-Bonsu, G., Lietard, A., Tozer, D. J. & Verlet, J. R. R. Low energy electron impact resonances of anthracene probed by 2D photoelectron imaging of its radical anion. J. Chem. Phys. 152, 174303 (2020).

    Article  CAS  PubMed  Google Scholar 

  32. Burrow, P. D., Michejda, J. A. & Jordan, K. D. Electron transmission study of the temporary negative ion states of selected benzenoid and conjugated aromatic hydrocarbons. J. Chem. Phys. 86, 9–24 (1987).

    Article  CAS  Google Scholar 

  33. Gallup, G. A. Stable negative ions and shape resonances in a series of organic molecules. J. Chem. Phys. 139, 104308 (2013).

    Article  CAS  PubMed  Google Scholar 

  34. Carelli, F., Gianturco, F. A., Satta, M. & Sebastianelli, F. Attaching electrons to a 3-ring acene: structures and dynamics of anions in gas-phase anthracene. Int. J. Mass Spectrom. 365–366, 377–383 (2014).

    Article  Google Scholar 

  35. Kregel, S. J., Thurston, G. K. & Garand, E. Photoelectron spectroscopy of anthracene and fluoranthene radical anions. J. Chem. Phys. 148, 234306 (2018).

    Article  PubMed  Google Scholar 

  36. Schiedt, J. & Weinkauf, R. Photodetachment photoelectron spectroscopy of mass selected anions: anthracene and the anthracene–H2O cluster. Chem. Phys. Lett. 266, 201–205 (1997).

    Article  CAS  Google Scholar 

  37. Campbell, E. E. B. & Levine, R. D. Delayed ionization and fragmentation en route to thermionic emission: statistics and dynamics. Annu. Rev. Phys. Chem. 51, 65–98 (2000).

    Article  CAS  PubMed  Google Scholar 

  38. Andersen, J. U., Bonderup, E. & Hansen, K. Thermionic emission from clusters. J. Phys. B At. Mol. Opt. Phys. 35, R1 (2002).

    CAS  Google Scholar 

  39. Adams, C. L., Hansen, K. & Weber, J. M. Vibrational autodetachment from anionic nitroalkane chains: from molecular signatures to thermionic emission. J. Phys. Chem. A 123, 8562–8570 (2019).

    Article  CAS  PubMed  Google Scholar 

  40. Kokubo, S., Ando, N., Koyasu, K., Mitsui, M. & Nakajima, A. Negative ion photoelectron spectroscopy of acridine molecular anion and its monohydrate. J. Chem. Phys. 121, 11112–11117 (2004).

    Article  CAS  PubMed  Google Scholar 

  41. Castro, K. P. et al. Incremental tuning up of fluorous phenazine acceptors. Chem. Eur. J. 22, 3930–3936 (2016).

    Article  CAS  PubMed  Google Scholar 

  42. Bakker, H. J., Rezus, Y. L. A. & Timmer, R. L. A. Molecular reorientation of liquid water studied with femtosecond midinfrared spectroscopy. J. Phys. Chem. A 112, 11523–11534 (2008).

    Article  CAS  PubMed  Google Scholar 

  43. Maldoni, M. M., Egan, M. P., Robinson, G., Smith, R. G. & Wright, C. M. The phase of H2O ice and the librational band in OH231.8+4.2: new interpretations. Mon. Not. R. Astron. Soc. 349, 665–677 (2004).

    Article  CAS  Google Scholar 

  44. Bull, J. N., West, C. W. & Verlet, J. R. R. On the formation of anions: frequency-, angle-, and time-resolved photoelectron imaging of the menadione radical anion. Chem. Sci. 6, 1578–1589 (2015).

    Article  CAS  PubMed  Google Scholar 

  45. Nielbock, M. et al. The earliest phases of star formation (EPoS) observed with Herschel: the dust temperature and density distributions of B68. Astron. Astrophys. 547, A11 (2012).

    Article  Google Scholar 

  46. Rosu-Finsen, A., Lasne, J., Cassidy, A., McCoustra, M. R. S. & Field, D. Enabling star formation via spontaneous molecular dipole orientation in icy solids. Astrophys. J. 832, 1 (2016).

    Article  Google Scholar 

  47. Bates, D. R. & Herbst, E. in Rate Coefficients in Astrochemistry (eds Millar, T. J. & Williams, D. A.) 41–48 (Springer, 1988).

  48. Rogers, J. P., Anstöter, C. S., Bull, J. N., Curchod, B. F. E. & Verlet, J. R. R. Photoelectron spectroscopy of the hexafluorobenzene cluster anions: (C6F6)n (n = 1–5) and I(C6F6). J. Phys. Chem. A 123, 1602 (2019).

    Article  CAS  PubMed  Google Scholar 

  49. Eppink, A. T. J. B. & Parker, D. H. Velocity map imaging of ions and electrons using electrostatic lenses: application in photoelectron and photofragment ion imaging of molecular oxygen. Rev. Sci. Instrum. 68, 3477–3484 (1997).

    Article  CAS  Google Scholar 

  50. Roberts, G. M., Nixon, J. L., Lecointre, J., Wrede, E. & Verlet, J. R. R. Toward real-time charged-particle image reconstruction using polar onion-peeling. Rev. Sci. Instrum. 80, 053104 (2009).

    Article  CAS  PubMed  Google Scholar 

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We thank M. McCoustra for useful discussions. This work has been funded by the EPSRC (EP/R023085/1 and EP/M507854/1).

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Authors and Affiliations



J.R.R.V. conceived the project. A.L. and G.M.-B. performed the experiments. A.L. analysed the data. All discussed the results and J.R.R.V. and A.L. wrote the paper.

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Correspondence to Jan R. R. Verlet.

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The authors declare no competing interests.

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Peer review information Nature Chemistry thanks Thomas Field, Xue-Bin Wang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Source data

Source Data Fig. 1

2D photoelectron spectra of PA(N)H water cluster anions.

Source Data Fig. 2

Energies of electronic states of PA(N)H water cluster anions.

Source Data Fig. 3

Photoelectron spectra of C14H10 and C14H10(H2O)3.

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Lietard, A., Mensa-Bonsu, G. & Verlet, J.R.R. The effect of solvation on electron capture revealed using anion two-dimensional photoelectron spectroscopy. Nat. Chem. 13, 737–742 (2021).

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