Imaging the translational dynamics of CF3 in liquid helium droplets

The translational dynamics of CF3 in liquid helium have been investigated by photodissociating CF3I dissolved in helium droplets consisting of several thousands of atoms. The velocity distribution of CF3 fragments that have escaped from the droplets has been determined using ion imaging techniques and is found to be considerably shifted to lower speeds with respect to the photodissociation of gas phase CF3I. The fragments furthermore show a speed dependent angular distribution that is isotropic for the slowest and approaches the gas phase distribution for the faster fragments. These distributions point to a nonthermal escape process in which, at least for the speeds relevant for the present experiment, the kinetic energy and momentum transfer from the fragments to the solvent appears to be governed by binary collisions with the individual helium atoms.