Recent experiments by Herek, Materny and Zewail [Chem. Phys. Lett. 1994, 228, 15] have demonstrated that the timing between two transform-limited, ultrafast laser pulses can be used to control the branching ratio of Na* (electronically excited atomic sodium) to Na in the photodissociation of NaI. In this work, we theoretically show that, by varying the linear chirp of the first pulse without changing its power spectrum or field strength versus time, the Na* to Na branching ratio can be controlled over a large range with a fixed interpulse delay time and a fixed form of the second pulse. Theory predicts that at 0 K the branching ratio can be varied by a factor of 3, while at high temperatures (1000 K), the factor drops to approximately 1.2 due to the effect of the wide distribution of initial states. Experimental results at 1000 K are presented and are found to be consistent with theory. Several possible experimental methods are discussed to overcome the effects of the thermal distribution of initial states.