Desorption of CO from Ru(001) induced by near-infrared femtosecond laser pulses

Heterogeneous catalysis on the atomic scale

Information about the elementary processes underlying heterogeneous catalysis may be obtained by investigating well-defined single crystal surfaces. The success of this "surface science" approach for "'real" catalysis can be demonstrated, for example, with ammonia synthesis. The progress of catalytic reactions can be observed on an atomic scale by applying scanning tunneling microscopy and other surface physical techniques, as is shown with different examples in this paper: CO oxidation on a Pt(111) surface proceeds preferentially along the boundaries between adsorbed O and CO patches. Ru is practically inactive for the same reaction under lower pressure conditions but is transformed into RuO2 under atmospheric pressure conditions, where part of the surface Ru atoms function as coordinatively unsaturated sites (cus). In contrast, in the hydrogen oxidation reaction on Pt(111), an autocatalytic reaction step comes into prominence, and is responsible for the formation of propagating concentration patterns on the surface as a characteristic of nonlinear dynamics. Additionally, the limits of the concept of thermal equilibrium in surface rate processes are explored by applying ultrafast (femtosecond) laser techniques.

Broadband vibrational sum frequency generation spectroscopy of a liquid surface

An important advance in surface science has been the evolution of sum frequency generation to the application of studying surface structure and chemistry of liquid surfaces at the molecular-level by probing the vibrational signatures of surface molecules. Recently, broad-bandwidth sum frequency generation (BBSFG) spectroscopy has become an important tool for investigating gas-solid interfaces. BBSFG spectroscopy allows, theoretically, a surface sum frequency spectrum to be acquired within one pulse of the laser. In this paper, the viability of BBSFG to study inherently small nonlinear response interfaces and the time-resolving capability of this surface-selective technology are demonstrated. Presented here are the first published accounts of spectra from a liquid surface utilizing the broad-bandwidth sum frequency technology with acquisition times as low as 500 milliseconds.

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

A novel type of surface vibrational sum-frequency generation spectroscopy is presented that enables a highly specific measurement of the coupling of molecules on surfaces. With this doubly vibrationally resonant technique, two-dimensional vibrational spectroscopy of molecules on surfaces becomes possible. The technique is demonstrated for the C-O stretch vibration of CO on a ruthenium (001) surface. It allows for the determination of the intermolecular coupling strength of dipole-coupled CO molecules on the surface.

Direct observation of vibrational energy delocalization on surfaces: CO on Ru(001)

We report the experimental observation of the gradual transition from a local oscillator to a two-dimensional delocalized phonon, observed for the CO-stretch vibration of carbon monoxide adsorbed on a Ru(001) surface by means of broadband-infrared saturation sum-frequency spectroscopy. The data are theoretically reproduced by an exchange model with residence times of the excitation down to 2.5 ps.