Selectivity in the Laser-Induced Photochemistry of I2 + C2H2 in the Gas Phase

Article abstract of DOI:10.1021/ja00284a015

The reaction between I2 and acetylene has been carefully studied to establish its potential use for the separation of radioactive isotopes of iodine.The two possible photoproducts, cis- and trans-1,2-diiodiethylene, were prepared and then characterized by GC, GC-MS, and FTIR in both condensed and gas phases.For the first time the IR spectra of both cis and trans isomers in the gas phase are reported.Below the dissociation energy, when either the orto or para modifications of I2 were excited, only the trans isomer was found as a product.Studies conducted with isotopic mixtures of ¹²⁷I2, ¹²⁹I2 and ¹²⁷I, ¹²⁹I revealed that the reactio proceeds by the addition of iodine atoms to acetylene.The production of atoms leads to isotopic scrambling.Consequently, this reaction cannot be used to separate the isotopes of iodine, as previously postulated.