CO2 Laser Induced Chain Reaction of C2F4 + CF3I

Article abstract of DOI:10.1021/j100379a034

A pulsed CO2 laser was used to induce the telomerization of CF3I with C2F4 in gas phase.This is an exothermic radical chain reaction, producing CF3(CF2)nI with low n.A problem, previously considered unresolvable, exists at low pressure: Good primary quantum yield is in conflict with long chain length; for kinetic reasons the chain length is short, if initially a high yield of radicals is generated by IR multiphoton dissociation.Radical dimers dominate in this case.To avoid this undesired direction of the reaction, we applied a novel method: At high pressure theradicals are generated with delay only, so that their instantaneous concentration is always small.At 3 bar we attained quantum yields of 0.2 for the desired iodides, with selectivity of 80percent.This good selectivity is a consequence of the second-order termination, according to our analysis.The quantum yield is 100 times larger than previously reported for a CO2 laser induced reaction.It can be raised even more, if the exothermicity is used for further propagation.We only came close to this ignition threshold.With more laser energy in longer pulses, it could be reached.