ADSORPTION AND REACTION OF NITROMETHANE (CH3NO2) ON PT(111)

The adsorption of nitromethane (CH3NO2 and CD3NO2) on Pt(111) surfaces has been investigated. Temperature programmed desorption (TPD) mass s pectrometry, ultraviolet photoelectron spectroscopy (UPS) and high res olution electron energy loss spectroscopy (HREELS) were used to probe the adsorption bond strength and bonding geometry of the chemisorbed s tate, and also thermal decomposition reactions on the Pt(111) surface. Nitromethane is weakly chemisorbed on Pt(111) with an adsorption ener gy of ca 11 kcal mol(-1). Adsorption is mostly (>75%) reversible, but some nitromethane decomposition on Pt(111) does occur at low coverages . HCN, H2O, NO and CO were the primary gas phase products that were de tected in TPD as a result of this decomposition. The principal decompo sition pathway is via cleavage of N-O bonds, mostly leaving the C-N bo nd intact, rather than the isomerization of nitromethane to methyl nit rite (CH3ONO) on the surface. Consistent with the small adsorption ene rgy of molecular nitromethane, UPS and HREELS of the chemisorbed monol ayer show only small changes in the electronic structure and vibration al spectra of nitromethane compared to condensed phase results. HREELS data indicate that chemisorbed nitromethane adopts a 'pseudo-bidentat e' bonding geometry with C-s(yz) symmetry in which the two oxygens are coordinated inequivalently to the surface with the molecular axis til ted within the molecular plane. (C) 1997 Elsevier Science B.V.