We report results of our first-principles investigation on the energetics and electronic structures of bromine-adsorbed carbon nanotubes. While the bromine molecule binds preferentially to the outer wall of metallic nanotubes, the binding energy of adsorbed atomic bromines are found to depend on the radius as well as the energy gap. A recent experiment on the nanotube separation using bromines is discussed based on our computational data. The formation of strong C-Br chemical bonds at the zigzag edge of graphite demonstrates a close relationship between the density of states at the Fermi level and the binding strength. (C) 2005 Elsevier B.V. All rights reserved.