Sum Frequency Generation Investigation of Water at the Surface of H2O/H2SO4 and H2O/Cs2SO4 Binary Systems
Steve Baldelli, Cheryl Schnitzer, and Mary Shultz
Department of Chemistry, Tufts University, Medford, Massachusetts 02155
D.J. Campbell
Department of chemistry, College of the Holy Cross, Worcester, Massachusetts 01610
Chemical Physics Letters, 287,
143 - 147, 1998.
The vibrational structure of water at the air/solution interface of an ionic solution has been
obtained for the first time. Using vibrational sum frequency generation it is determined that
ions in solution have a large orientational effect on the structure of the surface water. Electrolytic
solutions, ionic in nature, cause water to be oriented into a more regular hydrogen-bonded network
through an electric double layer at the interface. In electrolytic solutions where molecular or
associated H2SO4 or Cs2SO4 species dominate, the surface water molecules are bound into
hydrate complexes. These effects are explained using hard soft acid base (HSAB) theory.
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