Glancing-angle Raman study of nitrate and nitric acid at the air-aqueous interface

Glancing-angle Raman spectra of aqueous KNO3 and HNO3 solutions were used to determine the degree of nitric acid dissociation, a, in the bulk and in the surface region. Our results suggest that a in the surface region is similar to that in the bulk and highlight the importance of water molecule availability to the dissociation process. Using the a's and the m-sym NO3- Raman intensities, we obtained an adsorption isotherm for NO3- to the surface region from which we calculated a Kads, of 0.19 +/- 0.03 L mol (1), implying that nitrate exhibits an almost neutral surface affinity. (C) 2011 Elsevier B. V. All rights reserved.