Samples were freshly prepared the day of each experiment in ultrapure water, pH 5.6, to have an absorbance of 1.0 at the excitation wavelength of 267 nm. Following one photon irradiation as described in the transient absorption spectroscopy methods, irradiated samples were analyzed by using a HPLC (Shimadzu LC-20AD) associated with a photodiode array (PDA) detector (Shimadzu SPD-M20A) at room temperature. A Synergi Fusion RP column (Phenomenex, 4 µm, 25 cm × 4.6 mm) was used to separate the parent chromophore from its photoproducts. A 10 µL aliquot of the irradiated solution was injected into the HPLC through a manual injector. Ultrapure water (pH 5.6) was used to elute the sample with a flow rate of 0.5 mL min -1 .