The molecular adsorption and thermal reaction of 1,2-dibromoethane (DBE) on Cu(111) has been studied using ultraviolet photoelectron spectroscopy, work function change (Delta Phi) measurements, low energy electron diffraction, and line-of-sight temperature programmed desorption. At 100 K, DBE adsorbs molecularly, exhibiting a decrease in work function of 0.86 eV at the completion of the monolayer. Layer-by-layer growth is observed up to two molecular layers, with further adsorption leading to the growth of tower crystallites. The first layer of DBE undergoes thermal decomposition at 125 K to give gaseous ethene and chemisorbed bromine in a ( root3 X root3)R30 degrees structure, which increases the work function of the surface by 0.58 eV. Chemisorbed bromine from partial decomposition of the first layer is found to stabilize the remaining DBE molecules in the decomposing layer, thereby arresting complete decomposition until a higher temperature. Subsequent decomposition of the stabilized DBE leads to ethene emission at 145 and 160 K for initial DBE coverages in the submonolayer and multilayer regime, respectively.