Experimental methods to investigate laser-induced surface reactions

Experimental methods to investigate laser-induced surface reactions 

Two distinct experimental approaches can be used for investigating photodissociation processes at the gas-solid interface, depending on the nature of the observable. In the first approach, speed, angular distribution, and internal excitation of the photofragments leaving the surface are measured. In the second approach, the photoproduct left behind at the surface is monitored. In the second approach, the standard tools of surface science are used. Surface photochemical studies usually require ultra-high vacuum (UHV) conditions, of the order 10 ° to 10 mbar. Initially, the adsorption and thermal behaviour of the molecule-metal system must be characterized. Various surface-science tools can be used to provide information about adsorption geometry, molecular structure and thermal chemistry of adsorbates. 

Typically, the UV light sources used for this type of experiment are continuous (CW) arc lamps and pulsed lasers. Arc lamps are low cost, easy to operate and provide, with band-pass filters or monochromators, tuneable radiation from the IR to the UV. It should be noted that the incident power provided by them is relatively low, and thus thermal reactions are minimized, as surface heating is negligible. 

To obtain dynamical information for a particular surface photochemical process, pulsed light sources are essential. The most widely used pulsed source is an excimer laser. Depending on the gas mixtures used, it 

CH26 LASER STUDIES OF SURFACE REACTIONS AN INTRODUCTION 

---