The photolytic cage effect of iodine in the gas phase

The laser flash photolysis of iodine has been studied over a wide pressure range in several bath gases. At low pressures the observed quantum yield for photolysis at 6943 Å is independent of the gas density, whereas at higher pressures the quantum yield decreases with increasing gas density. This phenomenon is discussed in terms of the cage effect, and the measured yields are compared with model calculations. The experiments also provide information on the second order rate constants for iodine atom combination.