Sum frequency generation (SFG)-surface vibrational spectroscopy studies of buried interfaces: catalytic reaction intermediates on transition metal crystal surfaces at high reactant pressures; polymer surface structures at the solid-gas and solid-liquid interfaces

SFG has been utilized to monitor the surface species present on platinum and rhodium crystal surfaces during catalytic reactions at atmospheric pressures. Ethylene hydrogenation to ethane, cyclohexene hydrogenation to cyclohexane and its dehydrogenation to benzene, and carbon monoxide oxidation to carbon dioxide have been studied while also measuring the turnover rates and the gas phase product distribution by gas chromatography. Strongly bound spectators, weakly bound reaction intermediates, and pressure-dependent changes in the chemical bonding of surface species have all been observed. SFG spectra of polyethylene and polypropylene show monolayer sensitivity and reveal temperature-dependent changes of surface structure, For polymer blends, the hydrophobic component segregates to the solid-air interface, and the hydrophilic component segregates at the solid-water interface. Changes in SFG spectra of polymer blends as a function of bulk concentration correlate with changes of contact angle. SFG is an excellent probe of surface-structure and surface-composition changes as the polymer interface is altered.