The adsorption and condensation of Hg(CH3)(2) on Pt(111) at 95 and 310 K: An UPS study

We have studied the adsorption and condensation of dimethyl mercury at 95 and 310 K with UPS, using He I and He II excitation. The advantage of these two excitation energies is a distinct dependence of Hg and C-H, C-Hg derived molecular orbitals on photon energy. The agreement between the multilayer and the gas phase spectra is good. In the monolayer range, at both temperatures, the positions of the carbon-induced orbitals are not representative of the intact molecule. At 95 K dissociative adsorption leads to the major formation of adsorbed methyl radicals. At 310 K, only a monolayer is adsorbed. In agreement with literature results, methyl radicals transform into ethylidyne (C-CH3) or CH2 radicals and other CxHy species. We attribute a faint feature seen at 95 K and a strong one at 310 K, both located at about 4.8-4.9 eV below the Fermi level, to the possible formation of C-C bonds. These ethylenic species may be the precursors of the polymeric deposit found previously during the homogeneous decomposition of dimethyl mercury, when wall effects are important.