Surface vibrational spectroscopy from ultrahigh vacuum to atmospheric pressure: adsorption and reactions on single crystals and nanoparticle model catalysts monitored by sum frequency generation spectroscopy

Vibrational sum frequency generation (SFG) spectroscopy has been developed to a stage of surface sensitivity that is comparable to the classical surfa ce science methods. SFG has been successfully employed to study a variety o f adsorbate-substrate interfaces and due to its surface-specificity it allo ws the study of adsorbates from submonolayer coverages up to atmospheric ga s pressure. A number of case studies is presented including adsorption, co- adsorption and reactions on single crystal surfaces and supported nanoparti cles. Studies of CO adsorption on Pt(111) and Pd(111) from 10(-7) to 1000 m bar have shown that the high pressure adsorbate structures were comparable with saturation structures obtained at low temperature in ultrahigh vacuum. No evidence for pressure-induced surface rearrangements was found. However , pronounced differences in the CO adsorbate structure on supported Pd nano particles and on Pd(111) were detected. It is further shown how polarizatio n dependent SFG can be employed to determine molecular orientations of CO a nd NO and how SFG is carried out during ethylene hydrogenation. Broadband t echniques allow the performance of time-resolved pump-probe SFG experiments and to take "snapshots" of the transient vibrational spectrum.