Abstract
In this paper we report an X-ray emission study of bulk aqueous sulfuric acid. Throughout the range of molarities from 1 M to 18 M the sulfur Kβ emission spectra from H2SO4 (aq) depend on the molar fractions and related deprotonation of H2SO4. We compare the experimental results with results from emission spectrum calculations based on atomic structures of single molecules and structures from ab initio molecular dynamics simulations. We show that the S Kβ emission spectrum is a sensitive probe of the protonation state of the acid molecules. Using non-negative matrix factorization we are able to extract the fractions of different protonation states in the spectra, and the results are in good agreement with the simulation for the higher part of the concentration range.
Highlights
In this paper we report an X-ray emission study of bulk aqueous sulfuric acid
One frequently appearing question in these works considers the dynamics of the protons, which may be very relevant from the point of view of atmospheric new particle formation[40,41]
We report on our study of the S Kβ emission spectra of aqueous sulfuric acid as a function of the H2SO4 concentration
Summary
The highest Kβ1,3 line loses intensity, and the Kβx and Kβ” lines gain spectral weight We assign this behavior to two phenomena: the protonation state of the acid and the effect of solvation. As one or two protons are added (Fig. 2(d,e)), breaking of the symmetry causes the orbital to change shape, which makes it allowed for decay by dipole transition This analysis applies strictly only to the high-symmetry geometry of SO24−, and, due to ensemble averaging, the transition becomes allowed in real systems, yet probably very weakly. The overall trends in the spectral changes from protonation state to other are explained by the spectrum calculations
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