Photodissociation of CFX=CHCl (X=H,F) at 193 nm by product translational spectroscopy

In this work, we have studied the photodissociation of CFX=CHCl (X=H,F) at 193 nm using product translational spectroscopy. Results show that while the photoelimination of fast Cl, slow Cl, HCl, and HF occurs for both molecules, the cleavage of the C=C bond is only measurable for CF2=CHCl. Among these, only the fast Cl product was detected with strong angular preference with respect to polarized laser light. Product translational energy distributions P(E-t) were measured for all dissociation channels. The difference in the P(E-t) distributions between three-centered (3C) and four-centered (4C) molecular elimination reactions was observed. The low recoil energy for 3C HCl elimination from CF2=CHCl strongly suggests that there is no concerted isomerization from :C=CF2 to FC=CF. Although we detected no primary C-F bond fission in the present study, a relatively large yield of the secondary dissociation products F+C2H2 was determined for the internally excited fluorovinyl radical CHCHF. The results are discussed in terms of either a direct or an indirect dissociation process arising from excitation to the pipi(*) state, and comparisons between the title molecules are included. (C) 2002 American Institute of Physics.