Nature of the chemical bond in transition: dissection of radical-molecule reactivity

A complete method for quantifying the Born-Oppenheimer barriers of radical--molecule abstraction reactions is derived from first principles with the dual objectives of analytical prediction and conceptual understanding. Expanding upon the work of Donahue et al. (J. Phys. Chem. A 1998, 102, 3923-3933) this treatment uses the strategic construction of reactant-like and product-like wave functions to evaluate the coupling between crossing diabatic states. The overall reaction coordinate is evaluated in a modular fashion, whereby each region is analyzed within the context of its governing physics.     

Photochemical aging of α-pinene secondary organic aerosol: effects of OH radical sources and photolysis

This study addresses photochemical aging of secondary organic aerosol (SOA) produced from α-pinene ozonolysis. The SOA is aged via hydroxyl radical (OH) reactions with first-generation vapors and UV photolysis. OH radicals are created through tetramethylethylene ozonolysis, HOOH photolysis, or HONO photolysis, sources that vary in OH concentration and the presence or absence of UV illumination. Aging strongly influences observed SOA mass concentrations, but the behavior is complex. In the dark or with high concentrations of OH, vapors are functionalized, lowering their volatility, resulting in an increase in OA by a factor of 2-3. However, with lower concentrations of OH under UV illumination SOA mass concentrations decrease over time. We attribute this decrease to evaporation driven by photolysis of the highly functionalized second-generation products. The photolysis rates are rapid, a few percent of the NO(2) photolysis frequency, and can thus be highly competitive with other aging mechanisms in the atmosphere.