The degradation excitation laser source of 267 nm was generated from the 800 nm fundamental beam, as previously described by Krul et al. The excitation pulse was reduced to a spot size of ∼3.0 mm (3.010 ± 0.005 mm) using the knife edge method; while the average energy of the excitation beam was attenuated to 2 J with use of a neutral density filter, for an estimated average quantum flux of 3.8 10 cm -2 s -1 , as described in more detail elsewhere. The samples were matched at 0.65 absorbance units in 1 cm cuvettes at excitation wavelength for all solvents. The homogeneity of the solutions was maintained throughout the experiment through use of a Teflon-coated magnetic stir bar and a magnetic stir plate set to 1400 rpm.