ASPECTS OF PULSE RADIOLYSIS AND GAMMA RADIOLYSIS OF ALKYL IODIDES AND THEIR MIXTURES

Liquid alkyl iodides have been subjected to pulse radiolysis and γ radiolysis. A 2-μsec electron pulse produces a broad transient absorption band with a peak near 400 nm, with Gε equal to 18,000, 26,000, and 34,000 for methyl, ethyl, and isopropyl iodides, respectively. This band disappears in a second-order reaction, and is considered to be mainly due to an iodine atom alkyl iodide charge-transfer complex. Its extinction coefficient at the maximum is 9000 1. mol-1 cm-1 for all three iodides. A weaker and more rapidly decaying absorption is seen in the region 650-750 nm attributable to a positively charged species. The band with the peak near 400 nm appears with the same intensity when dissolved oxygen is present, but the decay kinetics are different. In mixtures of methyl and isopropyl iodides its formation is a nonlinear function of composition. In solutions of isopropyl iodide in cyclohexane, the concentration dependence of the band suggests that the charge-transfer complex has its origin partly in an ion-recombination process. Initial yields of iodine and HI have been determined for the γ radiolysis of alkyl iodides. The yield of HI falls off rapidly with dose, reaching a plateau at high doses. In mixtures of liquid methyl and isopropyl iodides, the dependence of the iodine and HI yields on composition follows a similar curve to that of the band at 400 nm in the pulse radiolysis. The I2 and HI yields vary with composition of mixture in quite a different way at -196°.