Thermal decomposition of cycloparaffins (C5-C8) and normalparaflins (C5-C8) on a clean stepped Ni (755) surface was investigated by low-energy electron diffraction (LEED). Auger electron spec-troscopy (AES) and temperature programmed desorption (TPD). Hydrocarbons were exposed on the surface at 123 K, No ordered LEED pattern was observed for all hydrocarbons. These molecules decomposed completely on the surface and remained as surface carbon while heating up to 573 K. No other species than hydrogen and reactant hydrocarbons was observed during TPD measurement. The initial decomposition probabilities of hydrocarbons except cyclopentane depended solely on the desorption temperature of monolayer adsorption state of hydrocardons irrespective of the number of carbons or types of hydrocarbons, i. e., cyclo or normal.
