Caging of Cl atoms from photodissociation of CF2Cl2 in clusters.

We investigate the photodissociation dynamics of freon CF2Cl2 by velocity map imaging at 193 nm. The Cl fragment images are recorded in various expansion regimes corresponding to isolated molecules and molecules in rare gas clusters. The molecular kinetic energy distributions are dominated by a peak at Ekin(Cl) ≈ 0.97 eV corresponding to the direct C-Cl bond dissociation but they also reveal features at lower kinetic energies. Possible mechanisms leading to these slow Cl atoms are discussed. The photodissociation in clusters is investigated in two regimes: (i) small Ar clusters with the CF2Cl2 molecule embedded in approximately one solvation Ar layer; (ii) large Xen, n¯ ≈ 100-500, clusters with embedded CF2Cl2 molecules. In the former clusters we observe caging yielding the Cl fragments with zero kinetic energy and direct exit resulting in fragments with the kinetic energies corresponding to the fragments from isolated molecules. In the latter case (ii) only the caged Cl fragments are observed.