Thermal and photo-induced dissociation of (C2H5)(2)Zn on Rh(111) surface

The adsorption and dissociation of (C2H5)(2)Zn were studied on Rh(111) surf ace. The methods used included X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS), Auger electron spec troscopy (AES), temperature-programmed desorption (TPD) and work function m easurements (Delta phi). Diethyl zinc adsorbs predominantly irreversibly on an Rh surface and causes a work function decrease of 1.3 eV. At submonolay er coverage it dissociates even at 90 K. Thermal dissociation of adsorbed m onolayer occurs at 170-250 K very likely through the transient formation of C2H5-Zn. The final products of the thermal dissociation, Zn and C2H5 are c haracterized by Zn(2p(3/2)) binding energy at 1021.3 eV for atomically adso rbed Zn and by vibration losses at 510, 860, 1140, 1430 and 2900 cm(-1) for adsorbed C2H5. HREELS revealed the formation of adsorbed ethylene in di-si gma form, which transforms into ethylidyne at higher temperature. TPD measu rements showed the evolution of hydrogen, ethane and butene. The Zn adatoms formed interact strongly with the Rh above 400 K, and desorb with T-p = 86 0-915 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. (C) 1999 Elsevier Science B .V. All rights reserved.