Photodissociation of propargyl chloride at 193 nm

The photodissociation of propargyl chloride (C ₃H ₃Cl) has been studied at 193 nm. Ion imaging experiments with state-selective detection of the Cl atoms and single-photon ionization of the C ₃H ₃ radicals were performed, along with measurements of the Cl + C ₃H ₃ and HCl + C ₃H ₂ recoil kinetic energy distributions, using a scattering apparatus with electron bombardment ionization detection to resolve the competing Cl and HCl elimination channels. The experiments allow the determination of the Cl ( ²P _3/2) and Cl ( ²P _1/2) (hereafter Cl*) branching fractions associated with the C-Cl bond fission, which are determined to be 0.5 ± 0.1 for both channels. Although prior translational spectroscopy studies by others had concluded that the low velocity signal at the Cl+ mass was due to daughter fragments of the HCl elimination products, the present work shows that Cl atoms are produced with a bimodal recoil kinetic energy distribution. The major C-Cl bond fission channel, with a narrow recoil kinetic energy distribution peaking near 40 kcal/mol, produces both Cl and Cl*, whereas the minor (5%) channel, partitioning much less energy to relative kinetic energy, produces only ground spin - orbit state Cl atoms. The maximum internal energy of the radicals produced in the lowrecoil-kinetic-energy channel is consistent with this channel producing electronically excited propargyl radicals. Finally, in contrast to previous studies, the present work determines the HCl recoil kinetic energy distribution and identifies the possible contribution to this spectrum from propargyl radicals cracking to C ₃ ⁺ ions in the mass spectrometer.