Role of Organics in Regulating ClNO2 Production at the Air-Sea Interface.

We report measurements of the product yield for nitryl chloride (ClNO2) production following the reactive uptake of dinitrogen pentoxide (N2O5) to a wide variety of ambient seawater samples as well as seawater mimics. The ClNO2 yield, as measured for ambient seawater collected from both coastal and open ocean waters, was found to be both insensitive to chlorophyll-a, a marker for biological activity, and significantly lower (0.16-0.30) than that expected for equivalent salt-containing solutions (0.82 ± 0.05). Suppression in the ClNO2 yield can be induced by the addition of aromatic organic compounds (e.g., phenol and humic acid) to synthetic seawater matrices. In the case of phenol, surface tension measurements reveal that the surface phenol:chloride ratio can be enhanced by more than a factor of 100 as compared to bulk ratios for subtle changes in surface tension (<1.5 mN m(-1)), providing a mechanism to suppress ClNO2 production at low bulk phenol concentrations. We interpret measurements of the dependence of the ClNO2 yield on phenol using a kinetic model, where we confine the surface enhancement in phenol to the top 1 nm of the interface. Our results are most consistent with a model where N2O5 is ionized within the first three water monolayers (<1 nm), where the product nitronium ions react rapidly with interfacial phenol molecules. These results suggest that ClNO2 may not be formed at the air-sea interface at the yield expected for NaCl, and that the reactive uptake of N2O5 and the subsequent product yield of ClNO2 may serve as a unique probe for the composition of the interfacial region of the sea surface microlayer.

Scattering of water from the glycerol liquid-vacuum interface.

Molecular dynamics calculations of the scattering of D2O from the glycerol surface at different collision energies are reported. The results for the trapping probabilities and energy transfer are in good agreement with experiments. The calculations demonstrate that the strong attractive forces between these two strongly hydrogen bonding molecules have only a minor effect on the initial collision dynamics. The trapping probability is influenced to a significant extent by the repulsive hard sphere-like initial encounter with the corrugated surface and, only at a later stage, by the efficiency of energy flow in the multiple interactions between the water and the surface molecules.

Molecular beam scattering from liquid surfaces.

By means of controlled collisions of atoms and molecules with liquid surfaces, molecular beam experiments can be used to probe how gases stick to, rebound from, and exchange energy with molecules in the liquid phase. This report describes measurements of energy exchange in collisions between gases (neon, xenon, and sulfur hexafluoride) and polyatomic liquids (squalane and perfluoropolyether). Energy transfer depends critically on liquid composition and is more efficient for the hydrocarbon than for the perfluorinated ether.