CO+.(H2)N CLUSTERS - BINDING-ENERGIES AND MOLECULAR-PARAMETERS

Temperature-dependent equilibrium measurements of mass-selected Co+ ions reacting with H-2 were used to determine binding energies and entropies for Co+.(H-2)n clusters. Clusters with one to seven H-2 ligands were examined. The observed binding energies decrease with cluster size in a pairwise fashion. The first and second H-2's have roughly equal binding energies (18.2 and 17.0 kcal/mol); the third and fourth binding energies are also equal (9.6 kcal/mol); the fifth and sixth cluster binding energies are 4.3 and 4.0 kcal/mol; the seventh H-2 is very weakly bound (approximately 0.8 kcal/mol). The observed pattern and magnitude of the cluster binding energies can be largely explained with a simple model of electrostatic attraction and steric interference. The results on the first three clusters agree well with high-level calculations by Partridge et al. The calculations give valuable insight into the cluster bonding and structure and allow reasonable predictions of structures for all clusters.