Ultrafast vibrational dynamics of aqueous acetate and terephthalate

We study the vibrational population relaxation and mutual interaction of the symmetric stretch (νs) and antisymmetric stretch (νas) vibrations of the carboxylate anion groups of acetate and terephthalate ions in aqueous solution by femtosecond two-dimensional infrared spectroscopy. By selectively exciting and probing the νs and νas vibrations, we find that the interaction of the two vibrations involves both the anharmonic coupling of the vibrations and energy exchange between the excited states of the vibrations. We find that both the vibrational population relaxation and the energy exchange are faster for terephthalate than for acetate.