Laser photodissociation of IBr is used to observe the deactivation of spin-orbit excited Br(4(2)P(1/2)) (Br-*) by ground state atomic I(5(2)P(3/2)). The measured quenching rate constant is k(I)=1.9+/-0.2X10(-11)cm(3)/s. A total Br-* quenching rate due to both ground state Br(4(2)P(3/2)) and self-quenching by Br-* is observed following photodissociation of Br-2. The effective rate constant is more than 20 times smaller than k(I). The results are compared with Landau, Zener, Stueckelberg (LZS) calculations and other experiments. The consequence of the fast I atom quenching on photodissociation-pumped Br-* lasers is discussed.