[en] The photolysis of ethyl bromide was studied at 100 torr and 23⁰C using 253.7-nm radiation. In the pure system between 60 and 90 s at an absorbed light intensity of 8.3 x 10¹³ quanta/cm³ s the major products and their respective quantum yields are as follows: hydrogen bromide, 0.26; ethane, 0.40; ethylene, 0.028; 1,1-dibromoethane, 0.102; 1,2-dibromoethane, 0.0092; vinyl bromide, 0.009; 1,1,2-tribromoethane, 0.0027; methane, 0.00052; and methyl bromide, 0.00091. When 5 mol % oxygen is added, the quantum yields in this time period become the following: hydrogen bromide, 0.47; ethane, 0.00032; ethylene, 0.0081; 1,1-dibromoethane, 0.0040; 1,2-dibromoethane, 0.022; vinyl bromide, 0; 1,1,2-tribromoethane, 0; methane, 0.0001; and methyl bromide, 0.091. Bromine is also formed with a quantum yield of 0.22. At long photolysis times the HBr and C₂H₄ go into a stationary state, and the main photolysis products are C₂H₆ and 1,1-C₂H₄Br₂ with quantum yields of 0.24 and 0.17, respectively. The behavior of the system is interpreted based on a model involving C--Br rupture as the main primary process (phi = 0.8) with a substantial contribution of HBr elimination (phi = 0.2). Primary C₂H₅ . and Br . fragments abstract hydrogen from the substrate to produce mainly the 1-C₂H₄Br. radical. Net product formation involves reaction of radical species with Br₂ (present at low, steady-state concentration <10^-5 M), Br. atoms, or HBr. The dynamic behavior of the system was investigated by computer simulation and compared with experimental results. 2 tables, 7 figures