Electronically excited bromine atoms Br(42P½), generated from the vacuum ultra-violet flash photolysis of CF3Br, have been studied using kinetic spectroscopy in the vacuum ultra-violet. The collisional deactivation of these atoms to their ground state Br(42P) has been investigated for the gases N2, CO, CF4, H2, CH4, D2, D2O, H2O, O2 and NO and the efficiencies of collisional quenching found to be 1.1 × 10–5, 3.2 × 10–5, 9.5 × 10–4, 7.8 × 10–3, 1.4 × 10–2, 1.8 × 10–2, 4.9 × 10–2, 0.16, 0.16 and 0.22, for the gases in the above order. The mechanism of spin orbit relaxation of Br(42P½) and I(52P½) is discussed in reference to present data for the relaxation of these electronically excited atoms.