Flash Photolysis of Transient Radicals. 1. X2(1-) with X = Cl, Br, I, and SCN

Article abstract of DOI:10.1021/j100257a037

The radicals Cl2(1-), Br2(1-), I2(1-), and (SCN)2(1-) were prepared by photolysis of appropriate chemical systems with one laser and were subsequently photolyzed wuth a second laser.The first three species were photolyzed at 355 nm, and (SCN)2(1-) was photolyzed at 532 nm; I2(1-) was also photolyzed at 700 nm.In each case, dissociation into the fragments X and X(1-) was detected by a bleach in the absorption of X2(1-).The quantum yield for this process is about 0.1 except for Cl2(1-) where the value is 0.2.In no case was electron photodetachment observed.Observation of the recovery of the original absorption allowed the corresponding rate constant to be measured.The values for Cl + Cl(1-) (8E9/M*s) and SCN + SCN(1-) (9E9/M*s) have not previously been measured directly.In the case of Cl2(1-) the bleach in absorption does not completely recover and the loss of absorpion is dose dependent.Because the presence of acid allows a more complete recovery it can be concluded that the product Cl atom is photolyzed by a second photon to procedure OH and Cl(1-).The quantum yield was determined to be about 0.5. this photoreaction is direct experimental evidence that the absorption band of Cl involves charge transfer from solvent.Detailed analysis of the bleaching and recovery behavior at high Cl(1-) concantrations showed no time lag which could be attributed to the ²P_1/2Cl atom, implying a short lifetime for this species.