The 193 nm Photodissociation of 1,1- and 1,2-Difluoroethylene

The photodissociation of 1,1- and 1,2-difluoroethylene (DFE) at 193 nm was studied by measuring product translational energy distributions, P(ET), for the various product channels. The P(ET)'s are used to obtain information on the exit barriers, product internal energy, transition states, and the stability of intermediates in many of these channels. Significant differences in the P(ET)'s for three-centered elimination of HF to produce :CCHF and four-centered elimination of HF to give HC⋮CF were observed. These were attributed to differences in the exit barriers and transition states for the two types of elimination. This is the first reported study of the three- and four-centered H2 elimination pathways producing :CCF2 and FC⋮CF, respectively. Both reactions showed the presence of a small exit barrier. This work also gives the first detailed description of the H and F atomic elimination channels. The P(ET) for primary H atom elimination indicates a simple bond rupture mechanism; the P(ET) for secondary H atom elimination suggests that triplet product is formed. The P(ET)'s for F atom elimination indicate that •CHCHF is more stable than •CFCH2. Where appropriate, comparisons of the various DFE and ethylene photodissociation channels were made.