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 H3OC/ 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 H3OC/ ion-pair structure, which leads to the electron recombination with the H3OC 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 3 eV, 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.
CITATION STYLE
Lengyel, J., Pysanenko, A., & Fárník, M. (2017). Electron-induced chemistry in microhydrated sulfuric acid clusters. Atmospheric Chemistry and Physics, 17(22), 14171–14180. https://doi.org/10.5194/acp-17-14171-2017
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