Structure of the cetyltrimethylammonium surfactant at fused silica/aqueous interfaces studied by vibrational sum frequency generation.

Utilizing vibrational sum frequency generation (SFG), we characterized the structure of adsorbed cetyltrimethylammonium chloride (CTAC) at the silica/aqueous interface in the presence of 10 to 500 mM NaCl and as a function of surfactant surface coverage. For low ionic strengths (10 mM NaCl), results indicate that adsorbed aggregates do not change conformation with increasing surface coverage. Instead, the surfactant adsorbs as micelle-like structures at concentrations considerably lower than surface saturation and the CMC.

Atmospheric heterogeneous stereochemistry.

While many biogenic and anthropogenic organic constituents in the atmosphere are surface-active and chiral, the role of stereochemistry in heterogeneous oxidation chemistry in the atmosphere has not yet been evaluated. Here, we present nonlinear vibrational surface spectra of fused silica substrates functionalized with quinuclidine diastereomers during exposure to 10(11) to 10(13) molecules of ozone per cm(3) in 1 atm helium to model ozone-limited and ozone-rich tropospheric conditions. Kinetic studies show that diastereomers that orient their reactive C=C double bonds toward the gas phase exhibit heterogeneous ozonolysis rate constants that are 2 times faster than diastereomers that orient their C=C double bonds away from the gas phase.