Addition-insertion-elimination reactions of O(P-3) with halogenated iodoalkanes producing HF(v) and HCl(v)

The reaction of CH2ICF3 and other fluorinated or chlorinated iodoalkanes wi th O(P-3), generated by microwave discharge of O-2 or 193 nm photolysis of SO2, produces vibrationally excited HF(v) or HCl(v), as observed by steady state or time-resolved Fourier transform infrared (FTIR) emission spectrosc opy. This process occurs even in competition with possible pathways to form HOI or IO products. The proposed mechanism is an addition-insertion-elimin ation process. The nascent vibrational distribution of the HF(v) produced f rom O+CH2ICF3 is determined to be 0.58 +/-0.10, 0.29 +/-0.08, and 0.12 +/-0 .03 for v=1, 2, and 3, respectively, with an upper bound of 0.04 from a few observed lines of v=4. The monotonically decreasing vibrational distributi on suggests a reaction involving HF(v) elimination from an intermediate com plex. There are a number of possible single or multistep kinetic pathways t hat could produce HF(v) under these conditions. To determine the predominan t pathway that produces the observed HF(v), the dependence of the time-reso lved HF(v) emission signal on reactant concentrations is measured and compa red with kinetics simulations. The results suggest a single step mechanism involving initial O(P-3) attack on the iodine of the CH2ICF3, in a manner s imilar to the start of the reaction of O(P-3) with C2H5I that produces HOI. This is followed by insertion of the oxygen atom into the carbon-iodine bo nd of the CH2ICF3, producing an activated complex with sufficient energy to eliminate HF(v). (C) 2001 American Institute of Physics.