Figure 4

(top) Malinowski indicator (IND) function plot for PCA of group 1 and group 2 EXAFS spectra (solid and dotted lines, respectively). The component number at which the function minimizes determines the transition from significant to secondary components, and suggests that 3 model As species are required for least-squares fits to group 1 EXAFS but only 2 model As species for group 2 fits. Visualization of the first seven normalized components from group 1 (bottom, left) and group 2 (bottom, right) confirms the IND function results: significant components have a high signal-to-noise ratio and each account for a significant percentage (ca. 5%) of the total variance within the group. Within group 1, PC4 and 5 are at the limits of empirical significance, which is discussed further in the text.