A b i n i t i o studies on the stabilities of even- and odd-membered Hn+ clusters

Abstract

A b i n i t i o SCF and SD–CI calculations have been performed for the hydrogen positive ion clusters H n + with n = 3–9. The optimum structures of the clusters were all determined to consist of a nearly equilateral H3 + core surrounded by neutral H and/or H2 ligands at the apices. The most interesting new finding is that the even‐membered clusters with n = 4, 6, 8 have binding energies comparable to the odd‐membered clusters with n = 5, 7, 9. This result is striking since the odd‐membered clusters have been observed in a number of previous experiments; whereas no even‐membered H+ n clusters have ever been observed experimentally. The conclusion appears to be that kinetic (but not thermodynamic) factors preclude formation of H+ 4, and other even‐membered hydrogen ion clusters, in experiments performed to date. Our best calculations indicate that H4 + is stable by at least 5 kcal/mol relative to H3 ++H. The other H n + species studied have probable binding energies in the range 3–7 kcal/mol.