Adsorption and reaction of CO on the slightly oxidized Mo(100) surface

The adsorption and desorption of CO on the slightly oxidized Mo(100) surfac e at 120 K were studied by HREELS and TDS, It was found that three CO molec ular states existed on the slightly oxidized Mo(100) surface at 120 K, name ly CO terminally bonded on a top sites (<(nu)over tilde>(CO) = 2 016-2 050 cm(-1)), bonded in four-fold hollow sites with a tilted geometry (<(nu)over tilde> = 1 088 cm(-1)) and bonded in an inclined manner to a Mo atom throu gh the carbon end and further coordinated to another Mo atom through a pi-C O bond (<(nu)over tilde>(CO) = 1 680 cm(-1)) respectively. For the terminal ly bonded CO, heating the surface induced the dissociation at lower coverag e, At the higher coverage, however, heating the sample caused the dissociat ion occurring below 450 K and desorption (T-p = 319 K) simultaneously. For other two CO states, only dissociation could be detected during heating the surface. The chemisorbed carton and oxygen atoms produced from CO dissocia tion could be recombined to form CO to leave the surface at 928 and similar to 1 320 K.