Potential energy surfaces infrared laser excitation

Tunable visible and ultraviolet lasers were available well before tunable infrared and far-infrared lasers. There are many complexes that contain monomers with visible and near-UV spectra. The earliest experiments to give detailed dynamical infonnation on complexes were in fact those of Smalley et al [22], who observed laser-induced fluorescence (LIF) spectra of He-l2 complexes. They excited the complex in the I2 B <—A band, and were able to produce excited-state complexes containing 5-state I2 in a wide range of vibrational states. From line w idths and dispersed fluorescence spectra, they were able to study the rates and pathways of dissociation. Such work was subsequently extended to many other systems, including the rare gas-Cl2 systems, and has given quite detailed infonnation on potential energy surfaces [231. 

The purpose of this article is to review some of the current endeavors in this developing field. To maintain brevity, the focus is on recent studies carried out in our own laboratory and in conjunction with Professor M.T. Bowers at the University of California at Santa Barbara, with emphasis on the use of kinetic energy release distributions and infrared laser multiphoton excitation to probe potential energy surfaces for the reactions of atomic metal ions with alkenes and alkanes. 

With infrared lasers vibrational motions of adsorbed molecules or atom groups in the adsorption potential at the surface can be excited. The surface mobility of these excited vibrational modes is much higher than the mobility of molecules in the ground state. If the vibrational energy reaches the adsorption potential barrier, these atom groups can move nearly freely across the surface. They may collide with other molecules or they may be desorbed. This may allow a selective control of surface chemical reactions by selective excitation of surface potential vibrations. This has been demonstrated by DJIDJOEV et al. [14.10] who studied the stimulation of surface reactions between hydroxyl groups OH and amino groups NH2 on a silica surface by irradiation with a CO2 laser. 

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