We report experimental results of the enhancement of Si emission from the Si(100) surface by submonolayer Br adsorption and by the exposure to Br at exposure rates as low as 10-3 L/s. The results were explained in terms of selective breaking of bonds of atoms at defect sites by interaction with adsorbed Br atoms. Semi-empirical calculation of the emission rate per pulse as a function of laser intensity and Br exposure rate explained semiquantitatively the results of not only the low-coverage and low-exposure-rate experiments but also high-exposure-rate experiments under conditions employed in the conventional dry etching.