Adsorption and reactions of CH2I2 on Ru(001) surface

Abstract The adsorption and dissociation of CH 2 I 2 were studied at 110 K with the aim of generating CH 2 species on the Ru(001) surface. The methods used included X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and work function measurements. Adsorption of CH 2 I 2 is characterized by a work function decrease (0.96 eV at monolayer), indicating that adsorbed CH 2 I 2 has a positive outward dipole moment. Three adsorption states were distinguished: a multilayer ( T p =200 K), a weakly bonded state ( T p =220 K) and an irreversibly adsorbed state. A new feature is the formation of CH 3 I, which desorbs with T p =160 K. The adsorption of CH 2 I 2 at 110 K is dissociative at submonolayer, but molecular at higher coverages. Dissociation of the monolayer to CH 2 and I proceeded at 198–230 K, as indicated by a shift in the I(3d 5/2 ) binding energy from 620.6 eV to 619.9 eV. A fraction of adsorbed CH 2 is self-hydrogenated into CH 4 ( T p =220 K), and another one is coupled to di-σ-bonded ethylene, which — instead of desorption — is converted to ethylidyne at 220–300 K. Illumination of the adsorbed CH 2 I 2 initiated the dissociation of CH 2 I 2 monolayer even at 110 K, and affected the reaction pathways of CH 2 .