Baseline Shift
In several datasets, a wavelength-dependent baseline shift can be observed at the start of the reaction (Fig. 8). This wavelength-dependent increase in absorption occurs during the induction period of autoxidation, and is consistent with light scattering, possibly indicating the formation of nanoparticulate structures in the oil. The extent to which this scattering occurred did not obey any discernable pattern with respect to catalyst identity or concentration, suggesting a complex interplay of factors leads to this light scattering. Possible sources include: a) Co nanoparticles formed from the drier; b) reverse micelles formed from polar oxidation products of the natural antioxidants present in the oil; or c) a mixture of both a) and b). It is not possible to distinguish between these possibilities based on IR data alone, and further analysis of these possibilities is currently underway using model systems. Attempts to normalize the baseline using linear baseline corrections or a penalized least squares smoother(Eilers 2003) were made, but did not lead to any improvement in the global analysis. Despite the interference, global analysis fitting generated reasonable SAS and rate constants, demonstrating the advantages of including data from a wider variety of wavelengths.