ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Ultraviolet (UV) photodissociation experiments are carried out for Arn(HBr) clusters in which the HBr is adsorbed on the surface of the Arn, and also on isomers of these systems in which HBr is embedded within the rare-gas cluster. The mean size of the cluster distribution in the experiments is around n¯=130. The kinetic energy distribution (KED) of the hydrogen atoms that left the clusters is measured. Molecular dynamics (MD) simulations of the photodissociation of the chemically similar clusters Arn(HCl) are used to provide a qualitative interpretation of the experimental results. The clusters with embedded HBr give a very cold H-atom KED. The clusters with the surface-adsorbed HBr give a KED with two peaks, one corresponding to very low energy H atoms and the other pertaining to high energies, of the order of 1.35 eV. The theoretical simulations show that already for n=54, there is a strong cage effect for the "embedded" molecule case, resulting in slow H atoms. The surface-adsorbed case is interpreted as due to two types of possible adsorption sites of HX on Ar55: for a locally smooth adsorption site, the cage effect is relatively weak, and hot H atoms emerge. Sites where the HBr is adsorbed at a vacancy of Arn lead to "encapsulation" of the H atom produced, with a strong cage effect. A weak tail of H atoms with energies well above the HBr monomer excess energy is observed for the embedded case. Simulations support that this is due to a second photon absorption by recombined, but still vibrationally hot, HBr. The results throw light on the differences between the cage effect inside bulk structure and at surfaces. © 2000 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.481798
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