| Abstract
| - Aqueous acetic acid solutions have been studied by vibrational sum frequency spectroscopy (VSFS) in orderto acquire molecular information about the liquid−gas interface. The concentration range 0−100% aceticacid has been studied in the CH/OH and the CO/CO regions, and in order to clarify peak assignments,experiments with deuterated acetic acid and water have also been performed. Throughout the wholeconcentration range, the acetic acid is proven to be protonated. It is explicitly shown that the structure of awater surface becomes disrupted even at small additions of acetic acid. Furthermore, the spectral evolutionupon increasing the concentration of acetic acid is explained in terms of the different complexes of aceticacid molecules, such as the hydrated monomer, linear dimer, and cyclic dimer. In the CO region, the hydratedmonomer is concluded to give rise to the sum frequency (SF) signal, and in the CH region, the cyclic dimercontributes to the signal as well. The combination of results from the CH/OH and the CO/CO regionsallows a thorough characterization of the behavior of the acetic acid molecules at the interface to be obtained.
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