The corrosive adsorption of Br atoms on Pt(111) was studied by variable temperature STM, TPD and AES. Photoinduced dissociative electron attachment to adsorbed CH 3 Br at 193nm was used to dose hot Br anions onto the surface at 90K. Br formed two ordered structures on Pt(111): (3x3) and (3x3)R30 o . STM images showed that both structures can coexist at intermediate coverage. Photofragmentation of CH 3 Br produced Pt atom monovacancies on the Pt(111) surface which were attributed to abstractive attack by the hot Br anions. The initial monovacancy etching efficiency of the adsorbing Br anions was high, roughly 33%.