Mh. Nassir et al., COVERAGE DEPENDENCE OF CO DISSOCIATION ON CLEAN AND HYDROGEN PRESATURATED FE(100) SURFACE, Surface science, 312(1-2), 1994, pp. 115-123
A detailed thermal desorption spectroscopy (TDS) study of very low and
intermediate exposures of CO on clean and H-2 presaturated Fe(100) su
rfaces was conducted. At extremely low CO exposures, CO adsorbs only i
n the pi-bonded CO state at low temperature. Molecules in this state e
xhibit an extremely weak carbon-oxygen bond and exclusively undergo di
ssociation when the temperature is raised above 440 K. At higher cover
ages, both dissociation and desorption is observed around 440 K even t
hough all the molecules are still bound in the pi-bonded CO state at l
ower temperatures. A model describing the partitioning between desorpt
ion and dissociation is proposed in which the dissociation fragments d
isplace the strongly bound CO in the pi-bonded state. The stoichiometr
y of this reaction allows a maximum of one half of pi-bonded CO molecu
les to dissociate. Preadsorbed hydrogen strongly influences the ratio
of dissociation to desorption as a function of coverage and suggests t
hat hydrogen may induce island formation in the CO adlayer.