INDEX molecular beam studies

Chemisorbed NH3 dissociates much more readily and many authors have studied the kinetics of dissociation. Loffler and Schmidt have studied the kinetics under molecular beam conditions on a polycrystalline specimen and on several low-index faces of a single crystal [(111), (100), (110), (210)]. The rate between 330 and 930 °C is strongly retarded by hydrogen and can be fitted by a Langmuir-Hinshelwood expression with competitive H2 and NH3 adsorption. 

There are still a number of surface systems where the structure cannot be determined by LEED for theoretical and experimental reasons. High Miller-index surfaces, such as stepped or kinked surfaces, have layers separated by very small distances normal to the surface. The calculational tools normally used for LEED break down in this case, and no new approach has yet been developed to solve this problem. Experimental difficulties restrict the study of insulator surfaces, because of charging problems, and of molecular crystal surfaces, because of beam damage problems. 

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