Chlorine atoms, Cl 3p52PJ, were produced in a flow of argon carrier gas at total pressures between 0.5 and 5 Torr; bromine atoms, Br 4p52P, were formed by the rapid reaction of Cl atoms with Br2: Cl + Br2→ BrCl + Br. The kinetics of the following chemiluminescent reactions (the “halogen afterglows”) were investigated: Cl + Cl + M → Cl2B3Π(0+u)+ M, Br + Cl + M → BrCl B3Π(0+)+ M, Br + Br + M → Br2A3Π(1u), B3Π(0+u)+ M. Atomic resonance absorption in the vacuum ultraviolet was used to measure Cl and Br atom concentrations directly. Chemiluminescence intensities were measured at lower concentrations (e.g., 4 × 1013 [Cl] 5 × 1012 cm–3) than in previous work. Under these conditions, the kinetics were simplified by elimination or reduction of quenching by halogen atoms of the excited states of the diatomic halogen. Quantum efficiencies Φ for formation of excited state halogen molecules by atom recombination were estimated as follows: Cl + Cl + M, Φ= 0.043; Br + Cl + M, Φ= 0.038; Br + Br + M, Φ= 0.059. Photon emission rates and steady-state concentrations of excited Cl2 and BrCl were determined. Independent work on laser-induced fluorescence, involving defined quantum states of Cl2(B) and BrCl (B), has been used to formulate a model for the halogen afterglows. Overall third-order recombination is believed to occur by consecutive bimolecular steps: (i) two-body recombination regarded as inverse predissociation, followed by (ii) vibrational or rotational energy relaxation, leading to stabilisation of the newly-formed excited Cl2(or BrCl).