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

Abstract

Strong B(E1) transitions have been recently observed between states in the 180 nucleus which follow roughly the energy sequence of a dimolecular e + 14C rotator. These findings have been interpreted by Gai et al. as evidence for a molecular dipole degree of freedom being present in the 180 nucleus. However, this idea was contradicted by the results of a microscopic multichannel calculation performed by Descouvemont and Baye which was based on elastic e + ~4C and inelastic e + 14 C (2 +) many-body cluster wave functions. We have improved this study by performing a microscopic multichannel calculation including additionally a n + 170 many-body fragmentation in order to enlarge our model space by those shell model components which dominate the structure of the (positive parity) 180 ground state band. Like Descouvemont and Baye we find a positive parity e + 14C molecular band in 180 and, additionally, a rather strong collectivity in the lowest 1-, 3-, and 5-states in 180. However, since the internal structure is different within these states, the calculated states should not be interpreted as a negative parity e + 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 the tsO nucleus.

Clustering in Non-Self-Conjugate Nuclei

“…The α-cluster strength was found to be split between several same spin-parity states in 18 O. This is contrary to the GCM 17) and AMD-GCM 26) models where only one state with significant contribution from 14 C(g.s.…”

“…Due to splitting of α strength between several nearly equally strong same spin-parity states identification of the states that belong to the negative parity inversion doublet rotational band is not straightforward. Nature of the observed splitting of α strength in 18 O is not well understood at present.…”

“…The α-cluster structure of 4N (N = Z) nuclei has been studied extensively, however much less information is available on the α-cluster structure of non-self-conjugate N = Z nuclei. Experimental study of clustering in T = 1 spectrum of 10 B and in 18 O are reported in this contribution. §2.…”

“…In this study we extracted spectroscopic information on states in 18 O populated in 14 C+α elastic scattering with the primary goal to identify α-cluster rotational bands. The α-cluster structure of 18 O was studied at the Florida State University, John D. Fox Superconducting Accelerator facility using the Thick Target Inverse Kinematics (TTIK) technique. 27) A 42 MeV 14 C beam was directed into the scattering chamber filled with Helium gas.…”

“…The pattern continues for the 5 − spin-parity for which two dominant 5 − states with θ 2 α of 0.13 and 0.17 are found at 11.6 and 13.08 MeV respectively. It is obvious that α strength in 18 O is split about equally between several same spin-parity states. This finding contradicts the results of GCM and AMD+GCM calculations 17), 26) and is still not well understood theoretically.…”