Thermally stimulated desorption of neutral CF3 from CF3I on Ag(111)

The low temperature thermal chemistry of CF3I on Ag (111) presents an example of competing reaction pathways; molecular desorption vs desorption of radical CF3. Temperature programmed desorption and angle resolved temperature programmed desorption, complemented with Auger electron spectroscopy and low energy electron diffraction, were used to discern the mechanism of the CF3 radical desorption channel. CF3 desorption is limited to the first monolayer of CF3I; 0.75 ML CF3I is the coverage used for angular dependence measurements. At 90 K most of the CF3I adsorbs molecularly to the metal, but also present under these conditions are dissociative adsorption and thermal decomposition channels limited to C-I bond cleavage. The decomposition product, CF3, desorbs as a radical at high temperatures (similar to 320 K) with the I remaining on the surface until 850 K. At submonolayer CF3I coverages, thermal activation produces a low temperature (100-150 K) radical desorption channel. Results indicate that low temperature CF3 thermal desorption occurs via dissociative electron attachment to molecular CF3I, yielding radical CF3 and adsorbed iodine. (C) 1996 American Institute of Physics.