Covalently bound molecular structures in the alpha+O-16 system

Using the concept of covalent molecular orbitals for neutrons and the known properties of the local alpha + O-16 potential the formation of asymmetric molecular structures in neon isotopes is discussed. Experimental evidence for parity doublets in Ne-21 is reviewed and a corresponding band structure for the states in Ne-21 at moderate excitation energy of E-x = 0-8 MeV is proposed. The structure of some bands can be interpreted as consisting of a n instrinsic asymmetric (He-4 + O-16) structure bound by a covalent neutron in sigma and pi orbitals. An extension of the observed structures to symme tric molecular structures in isotopes of Mg and heavier nuclei is suggested . In particular shape isomers in isotopes of magnesium, namely (He)(2)O mol ecules, can be predicted and an extended Ikeda diagram is proposed.