Vibrational relaxation of NO3−(aq)

•Infrared transient absorption spectroscopy of aqueous nitrate after UV excitation.•Vibrational relaxation of aqueous nitrate dominated by intermolecular energy transfer.•Vibrational relaxation after return to ground state occurs on 2 ps timescale.

The vibrational energy relaxation following UV excitation of nitrate ions in aqueous solution is investigated by infrared transient absorption spectroscopy. The experiments show that after their return to the electronic ground state the nitrate ions relax to the vibration ground state with a time constant of 2 ps. The experimental data are compared to simulations of two relaxation scenarios in which the nitrate molecules either relax by intra-molecular vibrational redistribution or by inter-molecular energy transfer. The comparison suggests that the energy relaxation is dominated by the latter.

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