The gain of the CF3I iodine photodissociation laser is observed to decrease exponentially with time. The decay rate increases dramatically with a small increase in flashlamp energy. Assuming that the rise in the gas temperature increases as the flashlamp energy is increased, this indicates that the process causing the decrease in the gain has an activation energy. It appears that CF3I pyrolysis is the source of the loss in gain, and from the observed decay rate the gas temperature is calculated to be about 1200°K. Measurement of the late‐time iodine‐iodine recombination rate also yields this temperature. The stimulated‐emission cross section measured under the same conditions is (2.6±0.5)×10−18cm2.