Sum Frequency Generation of O−H Vibrations on the Surface of H₂O/HNO₃Solutions and Liquid HNO₃

Abstract

The surfaces of aqueous HNO3 solutions and liquid HNO3 are examined using sum frequency generation (SFG). A molecular-level picture of these atmospherically relevant systems is developed. Consistent with previous interpretations, an electric double layer comprised of subsurface anions and cations develops in 0.005x and 0.01x HNO3 solutions, where x = mole fraction. Compared to pure water, these solutions generate more SFG signal in the hydrogen-bonded region as water molecules respond to the subsurface electric field by aligning with the surface normal. At higher concentrations, 0.05x and 0.4x HNO3, ionic complexes or molecules sufficiently approach the surface to disrupt the hydrogen-bonding network and perturb the first water layer. Neither liquid nitric acid nor its solutions show a clear O−H.

Surface Structural Studies of Methane Sulfonic Acid at Air/Aqueous Solution Interfaces using Vibrational Sum Frequency Spectroscopy

“…13 " 15 The SF intensity drop to nearly zero observed at 3220 cm" 1 by Shultz and coworkers [16][17][18][19] is not observed in either our work or the studies by Shen and coworkers, 13 * 15 nor is the weakness of the intensity at 3550 cm" 1 . One possible explanation for the differences between the air/water spectra of Shultz and the other studies is that the former uses a nanosecond laser system instead of the picosecond lasers of this group and Shen.…”

“…Shultz and coworkers using a nanosecond laser system observe this peak at 3150 cm" 1 . [16][17][18][19] The intensity drop at 3600…”

Theoretical Modeling of Interface Specific Vibrational Spectroscopy: Methods and Applications to Aqueous Interfaces

“…44,45,53,59 (When light impinges on an interface, a SFG signal is generated. This signal is both reflected from the boundary and transmitted through the interface.)…”

Experimental and theoretical studies of the interaction of gas phase nitric acid and water with a self-assembled monolayer

“…25 Both theory and experiment suggest that nitric acid is not fully dissociated at the interface of aqueous solutions. [26][27][28][29][30][31][32][33][34] Indeed, recent results suggest that undissociated HNO 3 interacts very weakly with water. 33,34 Because of the presence of significant concentrations of water vapor in the lower atmosphere, there is an abundance of water available on surfaces such as roads, buildings, etc., as well as in airborne particles.…”