Implementing the theory of sum frequency generation vibrational spectroscopy: A tutorial review

The interfacial regions between bulk media, although often comprising only a fraction of the material present, are frequently the site of reactions and phenomena that dominate the macroscopic properties of the entire system. Spectroscopic investigations of such interfaces are often hampered by the lack of surface specificity of most available techniques. Sum frequency generation vibrational spectroscopy (SFS) is a non-linear optical technique which provides vibrational spectra of molecules solely at interfaces. The spectra may be analysed to provide the polar orientation, molecular conformation, and average tilt angle of the adsorbate to the surface normal. This article is aimed at newcomers to the field of SFS, and via a tutorial approach will present and develop the general sum frequency equations and then demonstrate how the fundamental theory elucidates the important experimental properties of SFS.