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Abstract:Heterogeneous nitrates photolysis is the trigger for many chemical processes occurring in the polar boundary layer and is widely believed to occur in a quasiliquid layer (QLL) at the surface of ice. The dipole forbidden character of the electronic transition relevant to boundary layer atmospheric chemistry and the small photolysis/photoproducts quantum yields in ice (and in water) may confer a significant enhancement and interfacial specificity to this important photochemical reaction at the surface of ice. Using amorphous solid water films at cryogenic temperatures as models for the disordered interstitial air/ice interface within the snowpack suppresses the diffusive uptake kinetics thereby prolonging the residence time of nitrate anions at the surface of ice. This approach allows their slow heterogeneous photolysis kinetics to be studied providing the first direct evidence that nitrates adsorbed onto the first molecular layer at the surface of ice are photolyzed more effectively than those dissolved within the bulk. Vibrational spectroscopy allows the ~3-fold enhancement in photolysis rates to be correlated with the nitrates' distorted intramolecular geometry thereby hinting at the role played by the greater chemical heterogeneity in their solvation environment at the surface of ice than in the bulk. A simple 1D kinetic model suggests 1-that a 3(6)-fold enhancement in photolysis rate for nitrates adsorbed onto the ice surface could increase the photochemical NO2 emissions from a 5(8) nm thick photochemically active interfacial layer by 30%(60)%, and 2-that 25%(40%) of the NO2 photochemical emissions to the snowpack interstitial air are released from the top-most molecularly thin surface layer on ice. These findings may provide a new paradigm for heterogeneous (photo)chemistry at temperatures below those required for a QLL to form at the ice surface.

Arrays of Ru, Pt, and PtRu one dimensional (1D) nanowires (NWs) and nanotubes (NTs) were prepared by electrodeposition through the porous structure of an anodic aluminum oxide (AAO) membrane. In each case, micrometer-long NW and NT were formed with an outer diameter of ca. 200nm , close to the interior diameter of the porous AAO membrane. Arrays of NW and NT can be formed by varying the metallic salt concentration, the applied potential, and the conductivity of the electrolyte. The Ru and Pt deposition rates were measured in the various deposition conditions, using an electrochemical quartz crystal microbalance. The mechanisms responsible for the formation of Ru and Pt NW and NT are discussed based on the observed deposition rates and models found in the literature. Finally, it is shown that arrays of PtRu alloy NT and NW can be readily prepared and their compositions can be varied over the whole compositional range by changing the metallic salt concentration of the electrodeposition bath.

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