The structures and stabilities of helium cluster ions

Previously published 2-body and 3-body terms for an n-valued representation of the potential functions of He n + have been used to examine the structures of larger clusters. For n = 3?8 the most stable structure has a linear He3 + core surrounded by weakly bound, nearly neutral atoms, with up to four lying in an equatorial plane. Such structures persist as metastable species up to n = 12. For n > 8 the most stable structure consists of a He2 + core with up to nine atoms closely attached. The first excited state is predicted to have a vertical excitation energy of between 5·5 eV and 5·9 eV, changing little with n. This is in broad agreement with experimental observations.