Microscopic multichannel calculation of the molecular dipole degree of freedom in the¹⁸O nucleus

Abstract

StrongB(E1) transitions have been recently observed between states in the¹⁸O nucleus which follow roughly the energy sequence of a dimolecular α+¹⁴C rotator. These findings have been interpreted by Gai et al. as evidence for a molecular dipole degree of freedom being present in the¹⁸O nucleus. However, this idea was contradicted by the results of a microscopic multichannel calculation performed by Descouvemont and Baye which was based on elastic α+¹⁴C and inelastic α+¹⁴C(2⁺) many-body cluster wave functions. We have improved this study by performing a microscopic multichannel calculation including additionally an+¹⁷O many-body fragmentation in order to enlarge our model space by those shell model components which dominate the structure of the (positive parity)¹⁸O ground state band. Like Descouvemont and Baye we find a positive parity α+¹⁴C molecular band in¹⁸O and, additionally, a rather strong collectivity in the lowest 1⁻, 3⁻ and 5⁻ states in¹⁸O. However, since the internal structure is different within these states, the calculated states should not be interpreted as a negative parity α+¹⁴C molecular band. In this perspective, the microscopic multichannel calculations do not support the hypothesis of a molecular dipole degree of freedom being present in the¹⁸O nucleus.