The absorbance of the sample solutions at the excitation wavelength were all matched at 1.1 and 1.65 during low intensity (average quantum flux of 1.7 × 10 17 cm -2 s -1 ) and high intensity (average quantum flux of 8.6 × 10 17 cm -2 s -1 ) TAS experiments, respectively. The homogeneity of the solutions in a 2 mm path length fused silica cell, was maintained by continuous stirring with a Teflon-coated magnetic stirbar. To minimize the putative contamination of the transient signals by the formation of any photoproducts absorbing at the excitation wavelengths, freshly prepared samples were used, and frequently refreshed over the course of data acquisition such that the absorption maximum of the samples at excitation wavelength did not decrease by more than 5 percent.