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

Nature Chemistry volume 13, pages 737–742 (2021)Cite this article

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Abstract

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 https://doi.org/10.5281/zenodo.4314369. 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 https://www.github.com/adinatan/PolarOnionPeeling (Matlab version) or http://www.verlet.net/research.html (Labview version).

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Acknowledgements

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

  1. Department of Chemistry, Durham University, Durham, UK

    Aude Lietard, Golda Mensa-Bonsu & Jan R. R. Verlet

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  1. Aude Lietard
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Contributions

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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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). https://doi.org/10.1038/s41557-021-00687-1

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