ADSORPTION OF CH3CL ON CLEAN AND CL-DOSED PD(100) SURFACES

The adsorption of methyl chloride on a Pd(100) surface has been investigated by ultraviolet photoelectron spectroscopy (UPS). electron energy loss spectroscopy (in the electronic range, EELS), temperature-programmed desorption (TPD) and work function change. CH3CL adsorbs with high sticking probability at 80-100K. UPS and TDS spectra suggest that the adsorption of CH3Cl is molecular at 100 K, with a little distortion of the corresponding gas-phase molecular electronic structure. No dissociation of CH3Cl was observed even up to 550 K. By means of TPD, we distinguished two adsorption states with desorption energies of 46.9 and 33.4 kJ/mol. The formation of a condensed layer at 105-110 K was also observed. Adsorption of CH3Cl caused a significant work function decrease, DELTA-phi = -0.91 eV, indicating a dipole with positive end pointed away from the surface. The effects of electronegative additives, preadsorbed Cl and O were also examined. Preadsorbed Cl caused a slight destabilization of adsorbed CH3Cl at lower concentration, prevented the adsorption of CH3Cl at higher concentration and facilitated the formation of a condensed layer. No such effect was experienced in the presence of preadsorbed O.