THERMAL AND PHOTOINDUCED DISSOCIATION OF CH2I2 ON CU(100) SURFACE

The adsorption and dissociation of CH2I2 were studied at 90-250 K with the aim of generating CH2 on the Cu(100) surface. The methods used in cluded XPS, UPS, TPD, AES, and work function measurements. Adsorption of CH2I2 is characterized by a work function decrease (0.1 eV at the m onolayer), indicating that adsorbed CH2I2 has a positive outward dipol e moment. Two adsorption states were distinguished: a multilayer and a n irreversibly adsorbed state. The adsorption of CH2I2 at 90 K is diss ociative at the submonolayer but is molecular at higher coverages. Dis sociation of the monolayer proceeded at 192-204 K, as indicated by a s hift in the I(3d(5/2)) binding energy from 620.5 to 619.7 eV. Illumina tion of the adsorbed CH2I2 at 90-95 K markedly enhanced the dissociati on. The primary products are adsorbed CH2 and I. CH2 is characterized by a C(ls) binding energy of 283.9 eV and by a photoemission signal at 5.4-5.6 eV. CH species reacted to form C2H4 at 160-230 K, which desor bed in a pseudo-first-order process with T-p = 240 K. The high peak te mperature suggests the formation of a more strongly adsorbed, very Lik ely di-sigma- bonded ethylene. The self-hydrogenation of CH2, observed on platinum metals, did not occur on Cu(100).