THERMAL AND PHOTOINDUCED DISSOCIATION OF C2H5I TO YIELD C2H5 ON A PD(100) SURFACE

The surface chemistry of ethyl iodide over a Pd(100) surface has been studied at 90-450 K with the aim of generating C2H5 Species. The methods used included Auger electron spectroscopy (AES), photoelectron spectroscopy (XPS and UPS), temperature-programmed desorption (TPD), and work function measurements. Ethyl iodide adsorbs molecularly on a Pd(100) surface at 90 K, and this adsorption is followed by a multilayer formation at high exposures. Adsorption Of C2H5I is characterized by a work function decrease (2.00 eV at monolayer), indicating that adsorbed C2H5I has a large, positive outward dipole moment. The thermal dissociation of adsorbed C2H5I occurs only around 160-170 K. Illumination of the adsorbed layer induced the dissociation even at 90-95 K. The primary products of dissociation, C2H5 and 1, were characterized by a C(Is) binding energy of 284.1 eV and by an I(3d5/2) binding energy of 619.7 eV. The C2H5 reacted to form C2H4 and C2H6 at 160-230 K. A fraction of the ethylene (PI-bonded form) desorbs, and another fraction (di-sigma-form) is transformed into a vinyl species, which decomposes only above 450 K.