What Does Second Harmonic Scattering Measure in Diluted Electrolytes ?

Abstract : We derive a theoretical expression of second-harmonic-scattering signal in diluted electrolytes compared to bulk water. We show that the enhancement of the signal with respect to pure water observed recently for electrolytes at very low dilution in the $\mu$-range is a mere manifestation of the Debye screening that makes the infinite-range dipole-dipole solvent correlations in 1/$r^3$ disappear as soon as the ionic concentration becomes finite. In q-space, this translates into a correlation function having a well- known singular behavior around $q$ = 0, that drives the observed ionic effects. We find that the signal is independent of the ion-induced long-range behaviour of the function < cos$\phi(r)$ > that has been discussed recently. We find also that the enhancement depends on the experimental geometry and occurs only for in-plane polarization detection, as observed experimentally. On the other hand, the measured isotope effect between light and heavy water cannot be fully explained.
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https://hal-cea.archives-ouvertes.fr/cea-01818645
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Submitted on : Tuesday, June 19, 2018 - 1:21:17 PM
Last modification on : Saturday, March 16, 2019 - 1:29:38 AM

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Daniel Borgis, Luc Belloni, Maximilien Levesque. What Does Second Harmonic Scattering Measure in Diluted Electrolytes ?. Journal of Physical Chemistry Letters, American Chemical Society, In press, 9, pp.3698-3702. ⟨https://doi.org/10.1021/acs.jpclett.8b01690⟩. ⟨10.1021/acs.jpclett.8b01690⟩. ⟨cea-01818645⟩

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