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

Abstract

The reaction of CH2ICF3 and other fluorinated or chlorinated iodoalkanes with O(3P), generated by microwave discharge of O2 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 spectroscopy. This process occurs even in competition with possible pathways to form HOI or IO products. The proposed mechanism is an addition–insertion–elimination process. The nascent vibrational distribution of the HF(v) produced from 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 distribution suggests a reaction involving HF(v) elimination from an intermediate complex. There are a number of possible single or multistep kinetic pathways that could produce HF(v) under these conditions. To determine the predominant pathway that produces the observed HF(v), the dependence of the time-resolved HF(v) emission signal on reactant concentrations is measured and compared with kinetics simulations. The results suggest a single step mechanism involving initial O(3P) attack on the iodine of the CH2ICF3, in a manner similar to the start of the reaction of O(3P) with C2H5I that produces HOI. This is followed by insertion of the oxygen atom into the carbon–iodine bond of the CH2ICF3, producing an activated complex with sufficient energy to eliminate HF(v).