Ultraviolet elimination of H2 from chloroethylenes

The elimination of H2 in the photodissociation of mono- and di-chloroethylenes was studied with a pump-and-probe technique. A 193 nm excimer laser was used to photodissociate the parent molecules, and a tunable dye laser was used to probe the H2 fragment by 2+1 resonance-enhanced multiphoton ionization (REMPI). The nascent rotational state distributions of H2(X 1Σ+g,v″=0–4) were extracted from the REMPI spectra, and were found to have Boltzmann-type distributions. The maximum and average translational energies for some of the rovibrational levels of H2 were measured using magic angle Doppler spectroscopy. The translational energy of the fragments plus the internal energy of H2 was found to exceed the available energy for a three-center elimination mechanism. It is concluded that a migration mechanism plays a significant role in H2 elimination.