Yeganeh Mohsen S, Dougal Shawn M, Silbernagel Bernard G
ExxonMobil Research and Engineering Company, Annandale, New Jersey 08801, USA.
Langmuir. 2006 Jan 17;22(2):637-41. doi: 10.1021/la0518905.
We report the first observation of sum frequency generation (SFG) photons on high-surface-area powders, critically important materials in heterogeneous catalysis. We utilize SFG in total internal reflection (TIR) geometry and show that the TIR-SFG approach markedly reduces the destructive interference associated with nonlinear optical spectroscopy of small particle surfaces, making SFG studies of high-surface-area powders possible. The index of refraction of materials and their distance from the TIR-SFG prism are key parameters in generating and detecting the sum frequency signal. We find that TIR-SFG is highly sensitive to capillary condensation. To demonstrate the capability of the TIR-SFG technique, we measure the thermodynamics of methanol adsorption and desorption on high-surface-area SiO2.
