Novel surface vibrational spectroscopy: Infrared-infrared-visible sum-frequency generation

A novel type of surface vibrational sum-frequency generation spectroscopy i s presented that enables a highly specific measurement of the coupling of m olecules on surfaces. With this doubly vibrationally resonant technique, tw o-dimensional vibrational spectroscopy of molecules on surfaces becomes: po ssible. The technique is demonstrated for the C-O stretch vibration of CO o n a ruthenium (001) surface. It allows for the determination of the intermo lecular coupling strength of dipole-coupled CO molecules on the surface.