Measurement of Bromide Ion Affinities for the Air/Water and Dodecanol/Water Interfaces at Molar Concentrations by UV Second Harmonic Generation Spectroscopy

Recent experimental and theoretical work has demonstrated that certain anions can exhibit enhanced concentrations at aqueous interfaces and that the adsorption of bromide is particularly important for chemical reactions on atmospheric aerosols, including the depletion of ozone. UV second harmonic generation resonant with the bromide charge-transfer-to-solvent band and a Langmuir adsorption model are used to determine the affinity of bromide for both the air/water and dodecanol/water interfaces. The Gibbs free energy of adsorption for the former is determined to be -1.4 kJ/mol with a lower 90% confidence limit of -4.1 kJ/mol. For the dodecanol/water interface the data are best fit with a Gibbs free energy of +8 kJ/mol with an estimated lower limit of -4 kJ/mol.