Raman spectrum of 250 mM DPA in H2O/NaOH at pH 12 (curve 1) and the net solvent, H2O/NaOH at pH 2 (curve 2). The energy spacing between the Raman bands at 1,569, 1,435, and 1,383 cm–1 is marked and will be referred to in the time-resolved CARS measurements.