KINETICS OF DESORPTION, ADSORPTION, AND SURFACE-DIFFUSION OF CO2 ON MGO(100)

The kinetics of desorption, adsorption, and surface diffusion of CO2 on a single crystal MgO(100) surface were investigated using laser induced thermal desorption (LITD) techniques. Isothermal and linear temperature ramp LITD experiments revealed that the CO2 desorption from MgO(1N)) followed coverage-dependent first order kinetics. Assuming a preexponential of r = 1 x 10(13) s1, the desorption activation energy varied from E(d) - 9.4 to E(d) = 7.1 kcal/mol as a function of surface coverage. This coverage dependence suggested repulsive interactions between adsorbed CO2 molecules. Adsorption experiments revealed an initial sticking coefficient that decreased with increasing surface temperature. This behavior was in quantitative agreement with the predictions of a simple precursor-mediated adsorption model. LITD measurements of surface diffusion indicated a surface diffusion coefficient for CO2 on MgO(100) at 100 K that was below the limits of detection of the LITD experiment. These results allowed an upper bound of D less-than-or-equal-to 1 x 10(-9) cm2/s to be assigned for the surface diffusion coefficient of CO2 on MgO(100) at 100 K.