The dissociative adsorption and hydrodechlorination Of CCl4 on a single crystal Ir(110) was investigated using temperature programmed desorption (TPD) and molecular beam techniques. In order to better understand the behavior of CCl4, the adsorption and reactivity of less chlorinated methanes are compared to that of CCl4. CCl4 dissociates on the clean surface with near unity probability at low surface temperatures and decreases very slightly with increasing surface temperature. CHCl3, CH2Cl2, and CH3Cl also dissociate on the clean surface with near unity probability at low surface temperatures, however, the adsorption probability of these molecules are more sensitive to the surface temperature. As the molecule becomes less chlorinated, the adsorption probability falls more rapidly with increasing surface temperature. The preadsorption of hydrogen does not significantly affect the adsorption probability of CCl4 or CHCl3. However, with the beta(2) adsorption state of hydrogen saturated, CH(2)Ch(2) and CH3Cl dissociatively adsorb with a small probability. Adsorption Of CCl4 on the hydrogen precovered surface was found to produce mainly CHCl3 with trace amounts of CH2Cl2 and CH4 (detected as CD4). Similarly, adsorbed CHCl3 will hydrodechlorinate to mainly CH2Cl2. Hydrodechlorination of CCl4 is favored at lower surface temperatures and at higher surface coverages of dissociatively adsorbed CCl4. (C) 2003 Elsevier Science B.V. All rights reserved.