Photodissociation of HCl and small (HCl)m complexes in and on large Arn clusters

Photodissociation experiments were carried out at 193 nm for single HCl molecules which are adsorbed on the surface. of large Ar-n clusters and small (HCl)(m) complexes which are embedded in the interior of these clusters. For the surface case the size dependence is measured for the average sizes =140-1000. No cage exit events are observed in, agreement with the substitutional position, of the molecule deeply buried in. the outermost shell. This result is confirmed by a molecular dynamics simulation of the pickup process under realistic conditions concerning the experiment and the interaction potentials. The calculations of the dissociation process employ the surface hopping model., For the embedded case the average sizes covered are =3 and 6 and =8-248. The kinetic energy of the H atom fragments is measured exhibiting peaks at zero and around 2.0 eV which mark completely caged and unperturbed fragments, respectively. The ratio of theses peaks strongly depends on the cluster size and agrees well with theoretical predictions for one and two closed icosahedral shells, in which the nonadiabatic coupling of all states was accounted for. (C) 2004 American Institute of Physics.