Thermal and photo-induced dissociation of (C sub 2 H sub 5 ) sub 2 Zn on Rh(111) surface

The adsorption and dissociation of (C sub 2 H sub 5 ) sub 2 Zn were studied on Rh(111) surface. The methods used included X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS). Auger electron spectroscopy (AES), temperature-programmed desorption (TPD) and work function measurements ( Delta phi ). Diethyl zinc adsorbs predominantly irreversibly on an Rh surface and causes a work function decrease of 1.3 eV. At submonolayer coverage it dissociates even at 90 K. Thermal dissociation of adsorbed monolayer occurs at 170-250 K very likely through the transient formation of C sub 2 H sub 5 -Zn. The final products of the thermal dissociation, Zn and C sub 2 H sub 5 are characterized by Zn(2p sub 3div by2 ) binding energy at 1021.3 eV for atomically adsorbed Zn and by vibration losses at 510, 860, 1140, 1430 and 2900 cm exp -1 for adsorbed C sub 2 H sub 5 . HREELS revealed the formation of adsorbed ethylene in di- sigma form, which transforms into ethylidyne at higher temperature. TPD measurements showed the evolution of hydrogen, ethane and butene. The Zn adatoms formed interact strongly with the Rh above 400 K, and desorb with T sub p = 860-915 K. Illumination of the molecularly adsorbed layer at 90-95 K enhances the extent of the dissociation to ethyl zinc. The possible pathways of the formation of different products are described.