Abstract
The interaction of water, 1,4 dioxane, and gaseous nitrogen dioxide, has been studied as a function of distance measured through the liquid-vapour interface by Raman spectroscopy with a narrow (<0.1 mm) laser beam directed parallel to the interface. The Raman spectra show that water is present at the surface of a dioxane-water mixture when gaseous NO2 is absent, but is virtually absent from the surface of a dioxane-water mixture when gaseous NO2 is present. This is consistent with recent theoretical calculations that show NO2 to be mildly hydrophobic.
Highlights
Kolb et al.[1] have presented a thorough review, up to 2010, of outstanding theoretical and experimental problems relating to the reactions of atmospheric trace gases, including NO2, with a variety of wet and dry surfaces, and it is clear that there are still many interesting problems that need to be investigated.A recent theoretical study[2] of the interaction of nitrogen dioxide with the surface of water led to the conclusion that, even though the binding energy of the O2N–OH2 complex was found to be 9.5 kJ mol−1, a factor of 2 larger than previously calculated, nitrogen dioxide is at least “mildly” hydrophobic
The experiments reported here do not require surface selectivity of the kind employed in the experiments of Donaldson et al.,[3–8] but exploit the ability of Raman spectroscopy with a narrow (
Measurements made at intervals of several days were in excellent agreement, which implies that any observed depletion of water in the surface layer was not merely the result of slow dissolving of NO2 from the gas phase
Summary
Kolb et al.[1] have presented a thorough review, up to 2010, of outstanding theoretical and experimental problems relating to the reactions of atmospheric trace gases, including NO2, with a variety of wet and dry surfaces, and it is clear that there are still many interesting problems that need to be investigated. Instead of taking part in hydrogen bonds, the oxygen atoms of NO2 were found to be repelled by water molecules, which led to an unexpected preferential orientation of NO2 at the surface, with the oxygen atoms pointing out of the interface, and suggested that, in a system with mixed solvents, the surface might be depleted of water This cast new light on the processes by which nitrous acid (HONO) is produced in the troposphere, indicated the need for an experimental test of the theoretical results, and provided the motivation for the present study. The experiments reported here do not require surface selectivity of the kind employed in the experiments of Donaldson et al.,[3–8] but exploit the ability of Raman spectroscopy with a narrow (
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