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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 22 | Copyright
Atmos. Chem. Phys., 17, 14171-14180, 2017
https://doi.org/10.5194/acp-17-14171-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 28 Nov 2017

Research article | 28 Nov 2017

Electron-induced chemistry in microhydrated sulfuric acid clusters

Jozef Lengyel1,2, Andriy Pysanenko1, and Michal Fárník1 Jozef Lengyel et al.
  • 1J. Heyrovský Institute of Physical Chemistry v.v.i., Czech Academy of Sciences, Dolejškova 3, 18223 Prague, Czech Republic
  • 2Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria

Abstract. We investigate the mixed sulfuric acid–water clusters in a molecular beam experiment with electron attachment and negative ion mass spectrometry and complement the experiment by density functional theory (DFT) calculations. The microhydration of (H2SO4)m(H2O)n clusters is controlled by the expansion conditions, and the electron attachment yields the main cluster ion series (H2SO4)m(H2O)nHSO4 and (H2O)nH2SO4. The mass spectra provide an experimental evidence for the onset of the ionic dissociation of sulfuric acid and ion-pair (HSO4 ⋅  ⋅  ⋅ H3O+) formation in the neutral H2SO4(H2O)n clusters with n ≥ 5 water molecules, in excellent agreement with the theoretical predictions. In the clusters with two sulfuric acid molecules (H2SO4)2(H2O)n this process starts as early as n ≥ 2 water molecules. The (H2SO4)m(H2O)nHSO4 clusters are formed after the dissociative electron attachment to the clusters containing the (HSO4 ⋅  ⋅  ⋅ H3O+) ion-pair structure, which leads to the electron recombination with the H3O+ moiety generating H2O molecule and the H-atom dissociation from the cluster. The (H2O)nH2SO4 cluster ions point to an efficient caging of the H atom by the surrounding water molecules. The electron-energy dependencies exhibit an efficient electron attachment at low electron energies below 3eV, and no resonances above this energy, for all the measured mass peaks. This shows that in the atmospheric chemistry only the low-energy electrons can be efficiently captured by the sulfuric acid–water clusters and converted into the negative ions. Possible atmospheric consequences of the acidic dissociation in the clusters and the electron attachment to the sulfuric acid–water aerosols are discussed.

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