Different Dynamics of CH and Cl Fragments from Photodissociation of CHCl in Clusters.

We investigate the photodissociation of CHCl at 193.3 nm using the velocity map imaging technique in (CHCl) clusters in comparison with isolated molecules. Our results for the isolated molecules are in excellent agreement with the previous study of Cl fragments, and we extend it by detecting also the CH(ν = 0) fragments. For the clusters, the Cl (and Cl*) and CH fragment images are dominated by intense central isotropic features. The corresponding kinetic energy distributions (KEDs) reveal significant differences in the CH and Cl fragment dynamics. While the CH fragments exhibit a very narrow near-zero kinetic energy peak, pointing to almost complete of CH fragments, the Cl (and Cl*) fragments show more structured KEDs extending all the way to the maximum available kinetic energy. The Cl KED spectra have a bimodal character with two broad peaks close to zero and around 0.6 eV. We observe a higher / signal ratio from the clusters compared to the monomers. This is attributed to an efficient quenching of the higher vibrationally excited ν states of the CH fragments generated in the photodissociation. Collisional quenching of these excited states in clusters enhances the detected CH(ν = 0) state. Finally, we determine the [Cl*]/[Cl] branching ratio for the photodissociation pathways in the clusters as ≈0.55 ± 0.15 compared to 0.86 for the isolated molecules, which is also attributed to the collisional quenching of the excited state in the clusters. The clusters and photofragment dynamics are discussed.