However, the possibility that this primary-carbon-centered radical is formed by hydrogen abstraction from the terminal group cannot be excluded.Another interesting feature of OGP and DGP sonolysis is shown in Figure 4, b and c. All of the spin-adduct concentrations increase up to a maximum value and then decrease as a function of surfactant concentration. The change in spin-adduct concentration is more pronounced in the case of the secondary-carbon-centered radical adducts. Even though the surface tension decrease is larger in DGP than in OGP solutions, at equal concentrations of surfactants,26 the yields of secondary-carbon-centered radical adducts are similar up to about 1 mM. A sharp decrease in the concentration of these radical adducts is observed near the corresponding cmc regions. This suggests that a possible relation between the rate at which this radical adduct is formed and the cmc could exist.Above the cmc the monomer, which is partitioning into the interface, stays essentially constant in concentration while the micelle formation in the bulk solution increases, thus competing against an increase in the surfactant localization at the interfacial region. This is analogous to what occurs at a "normal" air-water interface in surfactant solutions, where the surface tension levels off after the cmc due to the micellization process.When aqueous solutions of OGP and DGP containing DBNBS-

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