Nuclear Clusters and Covalent Molecules on the femto-scale

Nuclear clusters like α-particles light N = Z nuclei are the building blocks of nuclear molecules. With additional 'valence' neutrons, which find there place in quantum mechanical two-center orbits a variety of covalently bound states in nuclei have been established in the last decade: in isotopes of 9-12Be, 13-14C and 21Ne. More recently we have studied molecular states in 18,19,20O-isotopes using the (7Li,p) reaction on 12,13,14C targets at Elab(7Li) = 44 MeV. The systematics of the energies and cross sections show rotational bands with high moments of inertia. These are characteristic of large deformations or molecular structures where the clusters are well separated. Generally the large scale shell model calculations are unable to reproduce these cluster bands. With two clusters of different size (e.g. (14C x 4He), or (16O x 4He)) intrinsically reflection asymmetric shapes arise. The molecular structures appear as rotational bands split into parity inversion doublets.