Sum frequency generation (SFG)-surface vibrational spectroscopy studies ofburied 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 an d rhodium crystal surfaces during catalytic reactions at atmospheric pressu res. Ethylene hydrogenation to ethane, cyclohexene hydrogenation to cyclohe xane and its dehydrogenation to benzene, and carbon monoxide oxidation to c arbon dioxide have been studied while also measuring the turnover rates and the gas phase product distribution by gas chromatography. Strongly bound s pectators, weakly bound reaction intermediates, and pressure-dependent chan ges in the chemical bonding of surface species have all been observed. SFG spectra of polyethylene and polypropylene show monolayer sensitivity an d reveal temperature-dependent changes of surface structure, For polymer bl ends, 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 correl ate with changes of contact angle. SFG is an excellent probe of surface-str ucture and surface-composition changes as the polymer interface is altered.